I've been using SyncThing for years with my KeePassXC database without issues (including Android for use with Keepass2Android).

On the odd occasion it's been modified on two devices without a sync and SyncThing produces a sync-conflict file, a simple "Merge from database..." within KeePassXC happily pulls in the newer data from both databases to merge them again.

I use the Staggered File Versioning feature on at least one device + a separate backup mechanism to satisfy my paranoia about losing the database.