Yeah, I find synchronization the least of my problems with the Keepass family. The file format uses GUIDs internally for most changes and most conflicts are easily merged/fixed. The fact that it is synchronized as files gives a lot of flexibility in options. You can use whatever cloud file sync provider you trust that month, and you have the flexibility to switch providers as your trust model and/or threat model change.

Mobile OSes are finally making it easier for arbitrary "file" sharing between such apps. (The iOS Files app is finally "decent" for this compared to just a few years ago.)

A similar file sync option to Syncthing I like to point out is Resilio Sync, a P2P device-to-device "torrent-like" sync tool. Among other things it also supports "encrypted shares" that cannot read inside the share but can still participate as a "seed" in the torrent-like share. Resilio Sync is relatively a lot more closed/commercial than Syncthing, but it's torrent-based underpinnings make it sometimes much faster with large shares. (As with everything, trade-offs to be made based on your personal threat model.)