I thought Synology was a NAS, did it move to the cloud
Other issue with automating sync stop and start when calibre GUI starts and stops is this: when one closes calibre one might have some library content files open in content editors - calibre editor, Audacity, Sigil, Word, VirtualDub, WinRAR etc. Personally I would want to ensure I saved and closed those before any folder and file syncing started. .
BR