It is 2023 and Photos.app still provides no way to sort photos/movies by file size.
I ended up writing some AppleScript that displays the file sizes of images/movies in a specific album. It is also simple to create a shell script to examine the photo library contents directly but mapping the UUID-based filenames back to the names used in Photos.app is not straightforward (to me at least).
You can't even create a smart album based upon file size.
Why is there no native support for this in Photos.app/PhotoKit?
(And, yes, I have submitted many feature requests over the years)