Syncthing is very much not about having a centralised source of truth. It gives you options about how things sync - I usually start very paranoid when I set up a sync folder and store all versions of a file if the files are only small, but you can store staggered versions etc.

It will also store all conflicts, which you then can manually resolve.

Another option you have is send-only and receive-only folders.

Like I said, lots of options, a bit of learning but it looks like what you want.