Syncthing doesn't solve the problem OP is talking about. It's amazing software that works as long as you don't have to sync the same file edited on two machines

Syncthing doesn't solve the problem OP is talking about. It's amazing software that works as long as you don't have to sync the same file edited on two machines before they have a chance to sync. There is no logic, besides something using CRDTs, that can reliably resolve the conflicts in every situation when you just have two sets of bytes and nothing else. Even if you maintain "last synced" copies + the current latest version and use those to compare against the server there are still simple situations where the conflict resolution doesn't work and/or requires user input. Anything that requires user-input like that can't properly sync binary files without resorting to making a new "File (Conflicted 1).sqlite" which you now manually need to compare. It just isn't the same thing