I installed the v22 of Clang needed for UE5.3 and re-built Development Linux UE5 project (3 settings in Rider, 2 in VS). That did not solve the problem as indicated by some responses. I set bUseAutoRTFMCompiler false in AutoRTFMTests.Target.cs and it fixed some aspects but ran into others. I ended up having to delete the entire folder.
Epic, this module is marked as not-for-licensees so I am curious why it is included in the source drop. Or why there are not instructions for the AutoRTFMCompiler if it is intended for us.