Generally speaking, no… from the Syncthing FAQ:
Is Syncthing my ideal backup application?
No. Syncthing is not a great backup application because all changes to your files (modifications, deletions, etc.) will be propagated to all your devices. You can enable versioning, but we encourage you to use other tools to keep your data safe from your (or our) mistakes.
Syncthing could be used as part of a backup scheme, but really not intended to be the only component.
Some Syncthing users have been using its file versioning feature as a backup tool: https://docs.syncthing.net/users/versioning.html
Variations on the same theme pop up on the forum from time to time so some of the previous posts might also be of interest because they discuss syncing filesystem snapshots, database dumps, etc. Just a few in no particular order: