On the contrary. If there's one thing you should self-host is definetly password manager.

I don't see much reason not to self-host a properly built password manager like Vaultwarden or something similar? The clients keep a local encrypted copy of the vault, so the server only needs to be up for syncing. If it went down for a week, you probably wouldn't even notice unless you were saving new logins. And even if the server got hacked, everything on it is encrypted. Why do you think it should not be selfhosted?

Can’t relate. If you’re worried about you’re own reliability to keep it online, just keep paper backups

What? Why not?