Unknown Photos
My iPhone (8) and iPadPro have photos on them that aren’t mine and I have no idea how they got there. How can I fix this?
iPad Pro, iPadOS 15
See the article How to share albums in Photos on your iPhone, iPad, and Mac - Apple Support
Delete a shared album
- Open the shared album.
- Go to the People tab.
- Tap Delete Shared Album.
If you're looking at your list of shared albums, you can also tap Edit, then tap the Delete button 
to delete a shared album.
When you delete a shared album, it's automatically removed from all of your devices and the devices of your subscribers. If Public Website was enabled, the shared album is removed from the web too. Deleting a shared ablum permanently deletes all of its photos. Before continuing, make sure that you save any photos that you want to keep.