I thought your other comments about writing your own were sarcasm about how that's such a terrible situation if that's the kind of thing it would take.
But this one looks like you actually mean it? Yikes.
Major reason I don't use password managers that much.
> Do you use the same password on every site?
I use a password I can reconstruct in memory for sites I care about logging in by hand. If I don't, or don't mind resetting my password each time, I just use random garbage + whatever platform password manager is the one active today, with vague hopes that it'll still be there the next time I need to log in.
> How do you deal with data breaches?
Who ever cares about those? I'm yet to hear about anything impactful being released on those. It only matters if you actually do reuse the same e-mail/login and password combinations on both important sites and garbage sites. Which is something you should not. But 2FA and magic links tend to solve that vendor-side, these days.
I use KeepassXC and Syncthing. It's not a single password manager doing both the managing and syncing, but it works very well, and I sync between phone/laptop/desktop without any third parties.
Keepass database is an openly documented format, and there are several apps available on iOS that use it and can store the database in your iCloud (ie syncthing is not required, unless you need to sync to non-iOS devices)
Just search for keepass in the app store (Keepassium, KeePass Touch, Strongbox, ...)
Just like their iCloud Keychain API that lets apps secretly track users across app reinstalls and device resets.