Hi,
This likely happens because those extensions are specifically looking for the regular Visual C++ project backend. If you are using Clang IntelliSense, it completely replaces the regular C++ IntelliSense, so extensions that are not aware of the Clang IntelliSense won’t find it.
You could disable Clang IntelliSense via VisualGDB Project Properties (or via a switch on the Clang IntelliSense Diagnostics Console window), however this would reduce the quality of the code completion results, as the Clang IntelliSense is specifically designed to work the best with GCC-specific code.