I dont agree with many things apple does at all, and I also think their password manager has flaws like revealing usernames without authentification.
It is pretty handy though, to have a file where the entries are stored unencrypted, and if the password manager detects an entry it prompts to decrypt exactly that field, maybe with a fingerprint.
KeepassDX needs to run in the background and be completely unlocked to even detect apps or password fields.
Do you know any existing app that can do this?
Actually it’s not that big of a problem. All clients make a local copy of the server’s database when they sync. So even when the server is unavailable you still keep your local copy on your client. Every client of Bitwarden offers the option to export your whole database. This means you could easily use that to import your exported database to any other instance.
The only “big problem” I see is to learn how to self-host. Most people are not tech-savvy so they don’t know how to do it and don’t even want to learn it.