One option is to purge the device that’s going thru an OS refresh from all other connected devices and then re-add the upgraded device from scratch, which could be tedious depending on the number of sync folders and devices involved.
Another option is to back up the Syncthing configuration before wiping the device for the OS refresh and then restore the Syncthing configuration afterwards. For details regarding the default configuration locations on Linux, macOS and Windows, see the Syncthing Configuration page of the official documentation.
If, for some reason, I were to forget to do any of these 2 options, would I be able to remove a dangling device from the list of “the connected devices” of other ones afterwards? Meaning, one by one, from each one.
I see that yes: Edit → Delete. Right? But would I be able to re-use its original label/name, with no issues?