File icon shows but cannot access data on my MacBook Pro running macOS 12.7.6

I'm running Monterrey 12.7.6 on an oldish MacBook in connection with a 2Tb external hard drive.

I started digitising my (paper) photos a few months ago, then dragging the images from Photos into my Documents folder, and soon was notified that there was no more space. As a result, and in order to free up space, I moved most of my photo files (IMG_****) onto my ext HD and have been working there quite happily ... until a few days ago. [And I threw away most of the hard-copy photos after imaging them.]

I discovered that most of the files I'd created around 2 months ago now just show an icon on the EHD in Finder, and I can't open the photo file. Looking at the info, all of them show a number of megabytes followed by "(4kb on disk)", and the permissions are all correct.

Unfortunately, I deleted these photos from my photos library, and they've since been deleted by the system, so I can't re-import them.

In some cases, searching for the file found another example. Once I dragged the other file to the same folder, miraculously BOTH could be opened and I could view the photo in Preview. They even had the same name but appeared as different files.

Otherwise:

I ran a disk check across the EHD - everything was fine, so no corrupt disk.

I'd deleted the trash so often, so there was nothing there.

I looked in iCloud, but things are deleted after a month so no joy there.

I looked for hidden files, but no joy there.

I wasn't aware of Time Machine, so no joy there either.

Any helpful suggestions in how I can get back the content for hundreds of images would be very welcome.

[Re-Titled by Moderator]

Original Title: file icon shows but cannot access data