In Visual Studio 2017 to register custom check-in policies i would use privateregistry.bin located in %localappdata%\Microsoft\VisualStudio\15_..., and i would add keys to the following path:
\Software\Microsoft\VisualStudio\15......\TeamFoundation\SourceControl\Checkin Policies
i know that in 2019 The registry path is 16.... something.
i´ve checked the .bin file and there is an entry with the policie but it doesn't load our custom check-in policies in VS.
i´ve also checked the registry entry and there is no new entry for visual studio 2019.
i hope somebody can help me.