Using only non american oss is literally impossible.

Security is about making it harder for the bad guys to get to what you don’t want them to get to. If they were sufficiently determined, sure they could get to it, but it is another layer. And one they may not expect, or if they were not sufficiently trained, what to do about.

I carry a yubi key to unlock my password manager. (Probably shouldn’t have said that) If you have a form of 2fa they wouldn’t know about, that might help you

What distro? Works fine on mine

Kdenlive has always been good for me, but I prefer shotcut. It seems simpler for the smaller edits I do

Get a fair phone and dismantle it

If you are interested into dipping your toes into rust land there is a library called Iced that I have used before. I at least like it better tham pyqt