CMakeLists.txt:
[Important Note]: this CMakeLists.txt is additional to the main one it means project name is defined in main CMakeLists.txt

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++17")

set(SOURCE_FILES src/main.cpp)
find_package(Qt6Widgets REQUIRED)

add_executable(${PROJECT_NAME}_client WIN32 ${SOURCE_FILES})


if(WIN32)
    target_link_options(${PROJECT_NAME}_client PRIVATE -static -static-libgcc -static-libstdc++) #still requires lots of DLLs so the built app doesn't start on other PC
endif()
target_link_libraries(${PROJECT_NAME}_client Qt6::Widgets)

if(WIN32)
    add_custom_command(
            TARGET ${PROJECT_NAME}_client POST_BUILD
            COMMAND ${WINDEPLOYQT_EXECUTABLE}
            ARGS "$<TARGET_FILE:${PROJECT_NAME}_client>" --dir $<TARGET_FILE_DIR:${PROJECT_NAME}_client> --release --compiler-runtime
            WORKING_DIRECTORY $<TARGET_FILE_DIR:${PROJECT_NAME}_client>
            COMMENT "Running windeployqt on ${PROJECT_NAME}_client executable"
    )
endif()

Main CMakeLists.txt (if needed to view):

cmake_minimum_required(VERSION 3.5)
project(HIDDENNAME)

add_subdirectory(client)
#add_subdirectory(server)

What I used:
[Qt version]: offline version of Qt6 (was used for Mingw64 toolchain)
[OS]: Windows11
[toolchain]: Msys2/Mingw64
[Compilers]:

• gcc (C compiler)
• g++ (C++ compiler)