2019 VS MS build broken after install
You have msbuild 16.3 in the GAC, which is why things fail for you.
Please, ungac msbuild by running these commands:
(C:\Program Files (x86)\Microsoft SDKs\Windows\v10.0A\bin\NETFX 4.8 Tools\gacutil.exe)
gacutil /u "MSBuild, Version=15.1.0.0"
gacutil /u "Microsoft.Build.Conversion.Core, Version=15.1.0.0"
gacutil /u "Microsoft.Build, Version=15.1.0.0"
gacutil /u "Microsoft.Build.Engine, Version=15.1.0.0"
gacutil /u "Microsoft.Build.Tasks.Core, Version=15.1.0.0"
gacutil /u "Microsoft.Build.Utilities.Core, Version=15.1.0.0"
gacutil /u "Microsoft.Build.Framework, Version=15.1.0.0"