Hi,
VisualGDB does not use any special mechanism for Qt – it simply delegates the work to CMake, hence we do not have any special instructions for it.
Normally, CMake would pick it up automatically, as long as you resynchronize the sysroot via VisualGDB Project Properties -> Build Settings. If not, you may need to specify the CMAKE_PREFIX_PATH to point to the directory inside the toolchain where VisualGDB has copied the built Qt files.
You can set CMAKE_PREFIX_PATH via VisualGDB Project Properties -> CMake -> Extra Prefix Directories. If you are not sure about the exact value to set, please consider searching online for “qt cmake_prefix_path” for examples from Qt documentation and other discussions.