every time I try, Microsoft comes in a week later and discontinues the current framework in favor of something else.

This is the way.

I have nothing useful to add, as I noped-out to become a full web developer, for exactly this reason.

If I desperately needed to call into C++ libraries, I would just build the whole thing in C++. And you're right, it won't look modern.

That said, it sounds like you're asking the person running your app to give you an unprecedented amount of trust in the modern age (running locally, unsandboxed, running code from unmanaged libraries, presumably outside an app store ecosystem).

If you have users, in that situation, I'm guessing you have a deeply compelling solution.

And if I were in those shoes, I would build it 100% in C++ and let my users live with it looking old school. They'll notice the appearance once or twice, then they'll notice all the more important functionality for a lot longer.