There is a folder with documents. It syncs with Google Drive. Recently there was a small glitch and part files left. It had to be restored from the recycle bin. In this regard, there is a need to provide an additional way to implement backup.
It is necessary that specific folder will automatically be copied to some place (most likely external HDD) whenever it (in file folders) made any changes (i.e. as in Google Drive).
You want all of this happened in the background and does not disturb the user.
Plus, it would be great to include the ability to save deleted files.
I.e. if in the main directory (where backup is done) removed a file in the backup folder it must not delete, and must somehow "marked".