Are you sure all this is really necessary? I just use round sync to copy over the camera and whatsapp media folders over ssh/sftp to my SBC. Then once every several months I delete the files from these foldes which exceed a given mtime (using find in termux).

I take it as a personal preference to never delete a copy of a file I care about, until I have taken positive proof that it is copied safely where it belongs.

I have deep trust issues with commands that work on more than one file at a time.