I can’t speak for YubiKeys themselves, but I’ve been using an OnlyKey for years (which can emulate one). Works great for KeePassXC, but only because it can type the DB password (challenge-response unlock still requires the password). I haven’t used the YubiKey emulator very much, except with a few services that are much easier to use if you have one.

I think it’s great to have the option of securing things with a hardware key, and I think it’s a good investment in general. But as others have said, it’s probably not be the best choice for KeePassXC (but there are benefits). I would recommend an OnlyKey, but it seems the prices have gone way up and they’re sold out.