A password manager that is open source, self hostable, works on all platforms, and most of all, is good. Even the 'good', proprietary ones (1Password, Lastpass), just aren't very good.
I’ve tried every single KeePass implementation there is/was for iOS, and most of them I couldn’t get to work at all. Some would actually launch, but then wouldn’t function. I think I found one that kinda-semi-sorta functioned, but then it had limitations in the database formats it supported and I couldn’t find a suitable counterpart on macOS.
But then I think the entire KeePass universe has probably changed a few times since then, so I probably need to go back and exhaustively re-try all the available programs over again.
But as that matrix gets bigger and bigger, the permutations and combinations of all the possible variants with all the other possible variants becomes impossible to test.
OTOH, 1Password has a local database, multiple options for sync’ing the database, a first-class UI, good support from a great company, and it “Just Works” on all the platforms I care about.