delete ALL photos on iphone

Hi there.

I wanted to delete all photos on my iPhone. I failed.

iOS 14.7

iPhone 12 Pro

macOS Big Sur 11.5

I copied all the pictures via the digital pictures app (cable, connect, start the app, transfer). Then I deleted them all.

Some pictures left

I looked in the finder for my iPhone and go on fotos. I deactivate the synchronization of any photo.

Still some pictures left.

All pictures on my iPhone I cannot delete. I can duplicate, but this is it

I sort of believe it may have to do that I synched another Fotos library pictures to this iPhone but I cant recall which one and if I still have them.

So how can I delete all pictures of my iPhone without resetting it entirely?