-mt runs a build's projects concurrently inside a single MSBuild process https://github.com/dotnet/core/blob/main/release-notes/11.0/preview/preview7/msbuild.md#multithreaded-mode-progress

.github/workflows/build-frontends.yml

@@ -38,10 +38,10 @@ jobs:
       run: dotnet restore ILSpy.XPlat.slnf -p:RestoreEnablePackagePruning=false
 
     - name: Build Debug
-      run: dotnet msbuild ILSpy.XPlat.slnf -p:Configuration=Debug -bl:Debug.binlog
+      run: dotnet msbuild -mt ILSpy.XPlat.slnf -p:Configuration=Debug -bl:Debug.binlog
 
     - name: Build Release
-      run: dotnet msbuild ILSpy.XPlat.slnf -p:Configuration=Release -bl:Release.binlog
+      run: dotnet msbuild -mt ILSpy.XPlat.slnf -p:Configuration=Release -bl:Release.binlog
 
     - name: list files
       if: always()

.github/workflows/build-ilspy.yml

@@ -90,9 +90,9 @@ jobs:
 
     - name: Build
       run: >
-        dotnet build ILSpy.sln --no-restore
+        dotnet build -mt ILSpy.sln --no-restore
         -c ${{ matrix.configuration }}
-        /p:Platform="$env:BuildPlatform" /m
+        /p:Platform="$env:BuildPlatform"
 
     - name: Format check
       run: dotnet-format whitespace --verify-no-changes --verbosity detailed ILSpy.sln

build.ps1

@@ -7,4 +7,4 @@ param(
 )
 $ErrorActionPreference = 'Stop'
 $env:OPENSSL_ENABLE_SHA1_SIGNATURES = '1'
-dotnet build ILSpy.sln -c $Configuration "-p:Platform=Any CPU" @args
+dotnet build -mt ILSpy.sln -c $Configuration "-p:Platform=Any CPU" @args