I had a Hello Qt6 Widgets CMake project.

Then followed with F2 into the ui_mainwindow.h header file where I pressed F2 in the class name.

First I've got a cannot access file message box and after while Qt Creator crashed with:

Unhandled exception at 0x00007FF8CB4C93E4 (ClangCodeModel.dll) in qtcreator.exe: 0xC0000005: Access violation reading location 0x00000000000001B9. 

Screencast showcasing the problem here:

QtCreator8-ClangCodeModel-Crash.mp4