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Which threat model is good enough to store Passwords?
Really, any threat model is as a password manager is advised. Remembering multiple complex passwords is more difficult than one good complex, yet, easy to recall password. If you try to manage it all manually, the higher the chance your passwords will end up with a pattern -- or worse, simple.
Which Password management we need to use?
This is up to you, based on your own threat model and personal preference as both KeePass and Bitwarden are highly recommended password managers.