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Last time I looked into this, you really couldn't in a reasonably simple way. It was possible between two users, but more than two just caused issues with syncing.

Syncing between your own devices is still an easier problem to solve than syncing between different users. The database is just a file.

I use a self hosted Nextcloud, but you don't have to.

KeePassXC allows you to automate opening a database from the URL column. My family and I share a second database and open it from there, but it's super kludgy on any other device.

https://syncthing.net/

Syncthing

Lived like this years, never going to look back. Add mobile to the mix and you're screwed with conflicts and manual resolution.