Syncthing review
If I change a file on my laptop and the change reaches my desktop, I want to know where the previous copy went. Syncthing can keep it on the receiving device when file versioning is turned on for that folder. Which computer receives the change matters as much as which folder I share.
Set up the machine that receives the changes
File versioning is configured per folder and per device. For a folder where I edit on the laptop, I’d enable Simple File Versioning on the desktop that receives those edits. When a change from the laptop replaces or deletes a file on that desktop, Syncthing moves the old copy into the versions folder. Look for .stversions inside the shared folder unless you set another location. An edit made on the desktop itself does not create an old copy there through Syncthing.
Try it with a spare file
I’d make a separate test folder with one text file, let it sync, then change the text on the laptop. Once the new text reaches the desktop, I’d look for the earlier copy there and open it before using the setup on a real project. Syncthing’s own FAQ points out that deletions can propagate. For a writing project, Scrivener can keep a snapshot of a section before a rewrite, which is a different kind of history.
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Anabel’s take
I’d use the shared folder for the files I want on both machines. For finished work I can’t afford to lose, I’d keep a separate backup and make sure I can open a copy from it.