It’s a terrible idea because as opposed to for example a folder with five Word documents in it, the files are not independent. If you have two sides making concurrent changes Syncthing will “merge” the two and the result is not something that is consistent in the Git world. The result is a corrupt repository.
Use Git as Git is intended: using fetch and push.
You might think that you can make sure only one side makes changes at a time. You are replying to a thread where that didn’t happen. If you got here by any search related to Syncthing resolving sync conflicts in a git folder, you are doing it wrong.
Do not use Syncthing to sync Git repositories.
Seriously.
Do not.