Read Only Photos on iPhone 13

Pictures that are transferred through a cable from a computer are shown by Photos, but they're not "owned" by Photos. So these pictures can't be edited or deleted by Photos. The idea is that they are kept on the computer and transferred to the phone temporarily. One way to delete them is to use the computer to transfer an empty set of "pictures" to the phone, and the empty set will replace the others. In using iTunes for this, it may give the option to deselect the pictures that are already there. 

You may also be able to use Image Capture from the Applications folder to select pictures to delete.

Another way to get rid of all the non-deletable pictures is to momentarily turn on iCloud Photos. You get a scary warning that these will be deleted. When you say OK, then they're trashed, and Photos will start to transfer the other pictures to iCloud. But you can turn off iCloud and stop that before much happens.

If you want to save some of these non-deletable pictures, then you can use "Share" to save them to Files. Then re-import them from Files to create fully useable versions.