I was looking for a tool to sync my Mac to my QNAP NAS. Now I found SyncThing.
The following is installed: QNAP v1.23.1 Mac OS v1.23.0
I created a test folder and syncronized between the devices. On my Mac I can delete all files. On the QNAP I do not have the authorization via the Finder. But my user has read/write rights. If I create a file on the QNAP in the folder, it is also syncronized and I can also delete it on both sides (Mac and QNAP). But as soon as I add one to it on Mac, it syncs to QNAP but cannot be deleted from Finder.