Project .clang-format no longer works (since 12.0)

Per project .clang-format in the root of the project was working fine on 11.0.3. When upgrading to any 12.0 series QtCreator, it no longer works.

Also trying to replace the .clang-format in %APPDATA%\QtProject\qtcreator\clang-format\Qt (or custom) results in the clang-format file put into this directory getting replaced by something else by QtCreator when QtCreator is launched and the "Code Style" window is opened.

Setting "Use custom settings" checked or unchecked does not have any effect. Formatting mode is not "Use build-in indenter".