Curious how this is distinct from SimpleX.

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I’m amused by the spoilers tag used for a question about a movie that was released in 1986.

Usually, the reason is HACS

Not that I’m aware of. You’d interact with the password database via another app.

Based on your criteria, I would suggest you use something like Keepass with the DB synced via Nextcloud. This allows you access to the local DB file if NC goes offline.