I solved it. If QT6_MSVC points to <path to qt>/Qt/6.8.1/msvc2022_64 and then you add target_include_directories(ChessCMake PRIVATE ${Qt6_DIR}/include) to CMakeLists.txt, it works
<path to qt>/Qt/6.8.1/msvc2022_64
target_include_directories(ChessCMake PRIVATE ${Qt6_DIR}/include)