I use KeepassDX on family mobiles with Syncthing for copies between laptop and phones. What would i gain moving to Vaultwarden, knowing that i would never open my network to the outside world? It would be easier to manage for sure, as im having to setup phones and laotops myself in the family and worry that they do silly things like turn off syncthing. But what about offline access to passwords? Does Bitwarden mobile client keep a local copy of database until it can sync?
The problem is that syncing between devices is not implemented in KeePass itself but through an external tool (Nextcloud, Syncthing, or whatever else). The sync client will only see the ciphertext and won’t be able to tell which records have been changed, only that two different binary files have a common ancestor and are in conflict.
The most obvious solution is to lock and close the database when it’s not in use (which is a good practice from a security perspective too), and to sync immediately when it is changed.
Idk what to tell you, but to me the merging is definitely implemented inside keepass itself, Keepass asks me if I want to merge the external changes and does so well.