I have a feeling you are overthinking the Matrix key system.
- create account
- create password you store somewhere safe
- copy the key and store somewhere safe
- when signing on a new device, copy-paste the key
Basically it’s just another password, just one you probably can’t remember.
Most of the client apps support verifying a new session by scanning a QR code or by comparing emoji. The UX of these could be better (I can never find the emoji option on Element, but it’s there…). So if you have your phone signed in, just verify the sessions with that. And it’s not like most people sign in on new devices all the time.
I’d give Matrix a new look if I were you.
There’s occasionally something buggy, but the last time I ran Windows there were a lot of bugs too. They’re just abstracted away, which Linux DEs don’t do at all.
For me, it’s about choosing the bugs that bug me less. If Windows is working better for you, just run Windows. Internet points are not worth much.