I used to use syncthing to solve that problem, until the developer dropped the distribution because of the Google's anti-social behavior.

But the interface of every software on a phone is so atrocious that I have never actually seen any benefit from having a password manager there that I could copy stuff from. So now I just don't have it, and haven't seen any loss yet.

That said, I store way more low-value passwords on the Firefox manager (that is synchronized) than high-value ones on the offline manager.