diff --git a/applications/test/parallel-comm0/Test-parallel-comm0.C b/applications/test/parallel-comm0/Test-parallel-comm0.C
index c9dba8cadc..e8c8a1e5b9 100644
--- a/applications/test/parallel-comm0/Test-parallel-comm0.C
+++ b/applications/test/parallel-comm0/Test-parallel-comm0.C
@@ -122,7 +122,12 @@ int main(int argc, char *argv[])
         }
 
         Pout<< "local  procUsed " << procUsed << nl;
-        reduce(procUsed.data(), procUsed.size_data(), bitOrOp<unsigned>());
+        reduce
+        (
+            procUsed.data(),
+            procUsed.size_data(),
+            bitOrOp<unsigned int>()
+        );
         Pout<< "reduce procUsed " << procUsed << nl;
 
         // Identical size on all procs
@@ -146,7 +151,12 @@ int main(int argc, char *argv[])
         }
 
         Pout<< "local  uniform " << uniformity << nl;
-        reduce(uniformity.data(), uniformity.size_data(), bitOrOp<unsigned>());
+        reduce
+        (
+            uniformity.data(),
+            uniformity.size_data(),
+            bitOrOp<unsigned int>()
+        );
         Pout<< "reduce uniform " << uniformity << nl;
     }
 
diff --git a/applications/utilities/postProcessing/dataConversion/foamToVTK/convertLagrangian.H b/applications/utilities/postProcessing/dataConversion/foamToVTK/convertLagrangian.H
index cc533e3a9b..d1c10b9574 100644
--- a/applications/utilities/postProcessing/dataConversion/foamToVTK/convertLagrangian.H
+++ b/applications/utilities/postProcessing/dataConversion/foamToVTK/convertLagrangian.H
@@ -30,11 +30,7 @@ if (doLagrangian)
         nameOp<fileName>()
     );
 
-    if (UPstream::parRun())
-    {
-        // Synchronise cloud names
-        Pstream::combineReduce(cloudNames, ListOps::uniqueEqOp<word>());
-    }
+    Pstream::combineReduce(cloudNames, ListOps::uniqueEqOp<word>());
     Foam::sort(cloudNames);  // Consistent order
 
     for (const word& cloudName : cloudNames)
diff --git a/applications/utilities/postProcessing/lagrangian/particleTracks/particleTracksSamplerTemplates.C b/applications/utilities/postProcessing/lagrangian/particleTracks/particleTracksSamplerTemplates.C
index a29b40b69a..8312ca5124 100644
--- a/applications/utilities/postProcessing/lagrangian/particleTracks/particleTracksSamplerTemplates.C
+++ b/applications/utilities/postProcessing/lagrangian/particleTracks/particleTracksSamplerTemplates.C
@@ -75,10 +75,7 @@ Foam::label Foam::particleTracksSampler::setTrackFields
     {
         wordList fieldNames = obr.names<IOField<Type>>();
 
-        if (Pstream::parRun())
-        {
-            Pstream::combineReduce(fieldNames, ListOps::uniqueEqOp<word>());
-        }
+        Pstream::combineReduce(fieldNames, ListOps::uniqueEqOp<word>());
 
         for (const word& fieldName : fieldNames)
         {
diff --git a/src/OpenFOAM/db/IOobjectList/IOobjectList.C b/src/OpenFOAM/db/IOobjectList/IOobjectList.C
index 8ae7d52a5f..4439109d00 100644
--- a/src/OpenFOAM/db/IOobjectList/IOobjectList.C
+++ b/src/OpenFOAM/db/IOobjectList/IOobjectList.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
-    Copyright (C) 2016-2022 OpenCFD Ltd.
+    Copyright (C) 2016-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -39,7 +39,7 @@ void Foam::IOobjectList::checkObjectOrder
     bool syncPar
 )
 {
-    if (syncPar && Pstream::parRun())
+    if (syncPar && UPstream::is_parallel())
     {
         wordList objectNames(objs.size());
 
@@ -62,21 +62,21 @@ void Foam::IOobjectList::checkNameOrder
     bool syncPar
 )
 {
-    if (syncPar && Pstream::parRun())
+    if (syncPar && UPstream::is_parallel())
     {
         wordList masterNames;
-        if (Pstream::master())
+        if (UPstream::master())
         {
             masterNames = objectNames;
         }
         Pstream::broadcast(masterNames);
 
-        if (objectNames != masterNames)
+        if (!UPstream::master() && (objectNames != masterNames))
         {
             FatalErrorInFunction
                 << "Objects not synchronised across processors." << nl
                 << "Master has " << flatOutput(masterNames) << nl
-                << "Processor " << Pstream::myProcNo()
+                << "Processor " << UPstream::myProcNo()
                 << " has " << flatOutput(objectNames) << endl
                 << exit(FatalError);
         }
@@ -86,12 +86,8 @@ void Foam::IOobjectList::checkNameOrder
 
 void Foam::IOobjectList::syncNames(wordList& objNames)
 {
-    if (Pstream::parRun())
-    {
-        // Synchronize names
-        Pstream::combineReduce(objNames, ListOps::uniqueEqOp<word>());
-    }
-
+    // Synchronize names
+    Pstream::combineReduce(objNames, ListOps::uniqueEqOp<word>());
     Foam::sort(objNames);  // Consistent order
 }
 
@@ -331,7 +327,7 @@ Foam::wordList Foam::IOobjectList::allNames() const
 
 void Foam::IOobjectList::checkNames(const bool syncPar) const
 {
-    if (syncPar && Pstream::parRun())
+    if (syncPar && UPstream::is_parallel())
     {
         wordList objNames(HashPtrTable<IOobject>::sortedToc());
 
diff --git a/src/OpenFOAM/db/IOstreams/Pstreams/PstreamReduceOps.H b/src/OpenFOAM/db/IOstreams/Pstreams/PstreamReduceOps.H
index bf8e6f2f66..7c114a54e8 100644
--- a/src/OpenFOAM/db/IOstreams/Pstreams/PstreamReduceOps.H
+++ b/src/OpenFOAM/db/IOstreams/Pstreams/PstreamReduceOps.H
@@ -382,7 +382,8 @@ Pstream_CommonReductions(uint64_t);
 Pstream_FloatReductions(float);
 Pstream_FloatReductions(double);
 
-Pstream_BitwiseReductions(unsigned);
+Pstream_BitwiseReductions(unsigned char);
+Pstream_BitwiseReductions(unsigned int);
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
diff --git a/src/OpenFOAM/db/IOstreams/Pstreams/UIPstreamBase.C b/src/OpenFOAM/db/IOstreams/Pstreams/UIPstreamBase.C
index 0151f0ab04..c4d4b8def6 100644
--- a/src/OpenFOAM/db/IOstreams/Pstreams/UIPstreamBase.C
+++ b/src/OpenFOAM/db/IOstreams/Pstreams/UIPstreamBase.C
@@ -494,7 +494,7 @@ Foam::Istream& Foam::UIPstreamBase::read(char* data, std::streamsize count)
 
 Foam::Istream& Foam::UIPstreamBase::readRaw(char* data, std::streamsize count)
 {
-    // No check for format() == BINARY since this is either done in the
+    // No check for IOstreamOption::BINARY since this is either done in the
     // beginRawRead() method, or the caller knows what they are doing.
 
     // Any alignment must have been done prior to this call
@@ -505,7 +505,7 @@ Foam::Istream& Foam::UIPstreamBase::readRaw(char* data, std::streamsize count)
 
 bool Foam::UIPstreamBase::beginRawRead()
 {
-    if (format() != BINARY)
+    if (format() != IOstreamOption::BINARY)
     {
         FatalErrorInFunction
             << "stream format not binary"
diff --git a/src/OpenFOAM/db/IOstreams/Pstreams/UOPstreamBase.C b/src/OpenFOAM/db/IOstreams/Pstreams/UOPstreamBase.C
index 13bf32ade0..fca288d555 100644
--- a/src/OpenFOAM/db/IOstreams/Pstreams/UOPstreamBase.C
+++ b/src/OpenFOAM/db/IOstreams/Pstreams/UOPstreamBase.C
@@ -346,7 +346,7 @@ Foam::Ostream& Foam::UOPstreamBase::write
     std::streamsize count
 )
 {
-    if (format() != BINARY)
+    if (format() != IOstreamOption::BINARY)
     {
         FatalErrorInFunction
             << "stream format not binary"
@@ -366,7 +366,7 @@ Foam::Ostream& Foam::UOPstreamBase::writeRaw
     std::streamsize count
 )
 {
-    // No check for format() == BINARY since this is either done in the
+    // No check for IOstreamOption::BINARY since this is either done in the
     // beginRawWrite() method, or the caller knows what they are doing.
 
     // Previously aligned and sizes reserved via beginRawWrite()
@@ -378,7 +378,7 @@ Foam::Ostream& Foam::UOPstreamBase::writeRaw
 
 bool Foam::UOPstreamBase::beginRawWrite(std::streamsize count)
 {
-    if (format() != BINARY)
+    if (format() != IOstreamOption::BINARY)
     {
         FatalErrorInFunction
             << "stream format not binary"
diff --git a/src/OpenFOAM/db/IOstreams/Sstreams/ISstream.C b/src/OpenFOAM/db/IOstreams/Sstreams/ISstream.C
index 831f6485b6..cfc1deca0f 100644
--- a/src/OpenFOAM/db/IOstreams/Sstreams/ISstream.C
+++ b/src/OpenFOAM/db/IOstreams/Sstreams/ISstream.C
@@ -1061,7 +1061,7 @@ Foam::Istream& Foam::ISstream::readRaw(char* data, std::streamsize count)
 
 bool Foam::ISstream::beginRawRead()
 {
-    if (format() != BINARY)
+    if (format() != IOstreamOption::BINARY)
     {
         FatalIOErrorInFunction(*this)
             << "stream format not binary"
diff --git a/src/OpenFOAM/db/IOstreams/Sstreams/OSstream.C b/src/OpenFOAM/db/IOstreams/Sstreams/OSstream.C
index 4efc58d929..fd7baf3e9d 100644
--- a/src/OpenFOAM/db/IOstreams/Sstreams/OSstream.C
+++ b/src/OpenFOAM/db/IOstreams/Sstreams/OSstream.C
@@ -224,7 +224,7 @@ Foam::Ostream& Foam::OSstream::write(const char* data, std::streamsize count)
 
 bool Foam::OSstream::beginRawWrite(std::streamsize count)
 {
-    if (format() != BINARY)
+    if (format() != IOstreamOption::BINARY)
     {
         FatalIOErrorInFunction(*this)
             << "stream format not binary"
@@ -251,7 +251,7 @@ Foam::Ostream& Foam::OSstream::writeRaw
     std::streamsize count
 )
 {
-    // No check for format() == BINARY since this is either done in the
+    // No check for IOstreamOption::BINARY since this is either done in the
     // beginRawWrite() method, or the caller knows what they are doing.
 
     os_.write(data, count);
diff --git a/src/OpenFOAM/db/IOstreams/Tstreams/OTstream.C b/src/OpenFOAM/db/IOstreams/Tstreams/OTstream.C
index 030090d3d5..67d1703d7a 100644
--- a/src/OpenFOAM/db/IOstreams/Tstreams/OTstream.C
+++ b/src/OpenFOAM/db/IOstreams/Tstreams/OTstream.C
@@ -143,15 +143,14 @@ Foam::Ostream& Foam::OTstream::write(const double val)
 
 Foam::Ostream& Foam::OTstream::write(const char* data, std::streamsize count)
 {
-    if (format() != IOstreamOption::BINARY)
-    {
-        FatalErrorInFunction
-            << "stream format not binary"
-            << Foam::abort(FatalError);
-    }
+    // if (format() != IOstreamOption::BINARY)
+    // {
+    //     FatalErrorInFunction
+    //         << "stream format not binary"
+    //         << Foam::abort(FatalError);
+    // }
 
     NotImplemented;
-
     return *this;
 }
 
@@ -162,26 +161,24 @@ Foam::Ostream& Foam::OTstream::writeRaw
     std::streamsize count
 )
 {
-    // No check for format() == BINARY since this is either done in the
+    // No check for IOstreamOption::BINARY since this is either done in the
     // beginRawWrite() method, or the caller knows what they are doing.
 
     NotImplemented;
-
     return *this;
 }
 
 
 bool Foam::OTstream::beginRawWrite(std::streamsize count)
 {
-    if (format() != IOstreamOption::BINARY)
-    {
-        FatalErrorInFunction
-            << "stream format not binary"
-            << Foam::abort(FatalError);
-    }
+    // if (format() != IOstreamOption::BINARY)
+    // {
+    //     FatalErrorInFunction
+    //         << "stream format not binary"
+    //         << Foam::abort(FatalError);
+    // }
 
     NotImplemented;
-
     return true;
 }
 
diff --git a/src/OpenFOAM/db/options/IOstreamOption.C b/src/OpenFOAM/db/options/IOstreamOption.C
index 9be225b51c..08be738239 100644
--- a/src/OpenFOAM/db/options/IOstreamOption.C
+++ b/src/OpenFOAM/db/options/IOstreamOption.C
@@ -59,7 +59,7 @@ Foam::IOstreamOption::formatEnum
 
     if (!formatName.empty())
     {
-        if (formatNames.found(formatName))
+        if (formatNames.contains(formatName))
         {
             return formatNames[formatName];
         }
diff --git a/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.C b/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.C
index 08710c72fa..059aa20391 100644
--- a/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.C
+++ b/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.C
@@ -566,7 +566,7 @@ Foam::fileOperation::lookupAndCacheProcessorsPath
         // 3 : mixed empty/non-empty directory (after reduce)
         // Combines andOp<bool>() and orOp<bool>() in single operation
 
-        unsigned procDirsStatus = (procDirs.empty() ? 1u : 2u);
+        unsigned int procDirsStatus = (procDirs.empty() ? 1u : 2u);
 
         if (debug)
         {
@@ -576,7 +576,7 @@ Foam::fileOperation::lookupAndCacheProcessorsPath
 
         if (UPstream::parRun() && (!distributed() || syncPar))
         {
-            reduce(procDirsStatus, bitOrOp<unsigned>());  // worldComm
+            reduce(procDirsStatus, bitOrOp<unsigned int>());  // worldComm
 
             if (procDirsStatus == 3u)
             {
diff --git a/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalMeshData.H b/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalMeshData.H
index b9a70712c5..40af50afbe 100644
--- a/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalMeshData.H
+++ b/src/OpenFOAM/meshes/polyMesh/globalMeshData/globalMeshData.H
@@ -606,34 +606,6 @@ public:
             //  full parallel analysis to determine shared points and
             //  boundaries.
             void updateMesh();
-
-
-    // Housekeeping
-
-        //- Deprecated(2020-09) use ListOps::appendEqOp
-        //  Uses a different template parameter
-        //  \code
-        //      globalMeshData::ListPlusEqOp<labelList>()
-        //      ListOps::appendEqOp<label>()
-        //  \endcode
-        //
-        //  \deprecated(2020-09) - use ListOps::appendEqOp
-        template<class T>
-        struct ListPlusEqOp
-        {
-            FOAM_DEPRECATED_FOR(2020-09, "ListOps::appendEqOp")
-            void operator()(T& x, const T& y) const
-            {
-                label n = x.size();
-
-                x.setSize(x.size() + y.size());
-
-                forAll(y, i)
-                {
-                    x[n++] = y[i];
-                }
-            }
-        };
 };
 
 
diff --git a/src/Pstream/dummy/UPstreamReduce.C b/src/Pstream/dummy/UPstreamReduce.C
index 59c83338d4..a23eee4dfd 100644
--- a/src/Pstream/dummy/UPstreamReduce.C
+++ b/src/Pstream/dummy/UPstreamReduce.C
@@ -223,7 +223,8 @@ Pstream_CommonReductions(uint64_t);
 Pstream_FloatReductions(float);
 Pstream_FloatReductions(double);
 
-Pstream_BitwiseReductions(unsigned);
+Pstream_BitwiseReductions(unsigned char);
+Pstream_BitwiseReductions(unsigned int);
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
diff --git a/src/Pstream/mpi/UPstreamReduce.C b/src/Pstream/mpi/UPstreamReduce.C
index 52d15aefb1..d21a4e9a5b 100644
--- a/src/Pstream/mpi/UPstreamReduce.C
+++ b/src/Pstream/mpi/UPstreamReduce.C
@@ -311,7 +311,8 @@ Pstream_CommonReductions(uint64_t, MPI_UINT64_T);
 Pstream_FloatReductions(float, MPI_FLOAT);
 Pstream_FloatReductions(double, MPI_DOUBLE);
 
-Pstream_BitwiseReductions(unsigned, MPI_UNSIGNED);
+Pstream_BitwiseReductions(unsigned char, MPI_UNSIGNED_CHAR);
+Pstream_BitwiseReductions(unsigned int, MPI_UNSIGNED);
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
diff --git a/src/functionObjects/utilities/areaWrite/areaWriteImpl.C b/src/functionObjects/utilities/areaWrite/areaWriteImpl.C
index ebb1ce3cc6..00e4459a66 100644
--- a/src/functionObjects/utilities/areaWrite/areaWriteImpl.C
+++ b/src/functionObjects/utilities/areaWrite/areaWriteImpl.C
@@ -74,10 +74,7 @@ void Foam::areaWrite::performAction
         fieldNames = areaMesh.thisDb().names<GeoField>(fieldSelection_);
 
         // Synchronize names
-        if (Pstream::parRun())
-        {
-            Pstream::combineReduce(fieldNames, ListOps::uniqueEqOp<word>());
-        }
+        Pstream::combineReduce(fieldNames, ListOps::uniqueEqOp<word>());
         Foam::sort(fieldNames);  // Consistent order
     }
 
diff --git a/src/meshTools/multiWorld/multiWorldConnectionsObject.C b/src/meshTools/multiWorld/multiWorldConnectionsObject.C
index 2dc3d74dea..420f00aaa9 100644
--- a/src/meshTools/multiWorld/multiWorldConnectionsObject.C
+++ b/src/meshTools/multiWorld/multiWorldConnectionsObject.C
@@ -237,10 +237,7 @@ void Foam::multiWorldConnections::createComms()
     const label oldWarnComm = UPstream::commWarn(UPstream::commGlobal());
     const label oldWorldComm = UPstream::commWorld(UPstream::commGlobal());
 
-    if (Pstream::parRun())
-    {
-        Pstream::combineReduce(allConnections, worldConnectBitOrEq());
-    }
+    Pstream::combineReduce(allConnections, worldConnectBitOrEq());
 
     // Check for mismatched connections
     label brokenConnections = 0;