From the perspective of Syncthing: No.
From the perspective of KeePassXC: Probably not, but I guess it is more likely you get help in a KeePassXC forum.
I use Syncthing to synchronise KeePass databases and it does the job very well, but yeah, if you edit the database file on different machines simultaneously, you will get conflicts.
You may want to look up an easy way to merge KeePass databases, perhaps by a command line script or something in that manner.
I ended up using KeePass’s own synchronization functionality (although I use KeePass rather than KeePassXC), simply because that properly handles merging conflicts, and I didn’t want to risk locking myself out of somewhere due to a bad merge.
Not really on topic, but Syncthing can drain a phone battery pretty quickly if you’re on the move across areas with weak signal (e.g. the countryside), which will likely force it to disconnect and reconnect constantly.
KeePassXC can merge: Menu Database > Merge from Database. I need to do that every now and again if I do changes on the phone and pc at the same time ( (had the phone running only when charging, now all the time - no battery issues for me) .
I tried using keeshare and it should work, but unfortunately the Android clients don’t support keeshare. I’m using keepass2android.
A solution that requires zero user intervention would be nice.