Create the user who should run the service, or choose an existing one.(Skip if your distribution package already installs these files, see above.) From git location copy the syncthing@.service file into the load path of the system instance. On Debian 12, the path of the file is ‘/usr/lib/systemd/system’. I added the following line to the [Service] section of the file:

Group=users

Enable and start the service. Replace “myuser” with the actual Syncthing user after the @:

$ sudo systemctl enable syncthing@myuser.service
$ sudo systemctl start syncthing@myuser.service

Reference

https://docs.syncthing.net/users/autostart.html