Some extensions by Microsoft are proprietary (such as their C# debugger and C++ extension) and can only be used with VSCode. For other extensions, you may be able to use them. See the docs at https://github.com/VSCodium/vscodium/blob/master/DOCS.md#ext...

I didn't know about https://open-vsx.org/. Very nice! But besides those languages, they are also missing things like the remote ssh extension, which is a big deal breaker for me (and I assume many others regardless of language).