I had 2 laptops and was using syncthing to sync files across my Documents folder (local) on both. Unfortunately I gave the old laptop to someone else to use it and they didn’t factory reset the device and just deleted all the files in the document folder. How do I recover it? I’m not using any versioning on Syncthing.
This is outside of Syncthing at this point. If the data was critical, you basically need to immediately power the laptop off (i.e. literally just long-press the power button to shut it down forcefully). You then need to remove the storage drive, take it to another device, and then continue with data recovery there.
However, if you’ve got no previous experience with data recovery, you may be better off taking it to a specialised service. Please keep in mind that it won’t be cheap. I’m also assuming here that you can actually take the drive out and it’s not something soldered in. In that case, you could still attempt data recovery on the same device, e.g. by booting to live Linux environment, etc.
In short, the key point is that you must not write anything more to the drive in question, or otherwise you risk overwriting the previous data, rendering it unrecoverable. This includes just running the OS or other software, which also writes to the drive on their own. That’s why it’s critical to power it off as soon as possible.
I would also contact them if you still can and see if those files are in the recycle bin on the old machine. If so they can restore them and they should transfer back if syncthing is still running on both machines.