When I don't like a photo I took with my iPhone 11, I delete it (with the 'Photos' app), and empty the trash ('Recently Deleted' album).
Once in awhile I mount the phone under Linux and backup my photos by copying the DCIM subdirectory. When I do this I notice that there are many duplicates (just an annoyance) and many photos that I assumed had been deleted. However, the deleted photos don't show up in Photos nor in iCloud.
What is going on here?