The relevant app review rules are:
"2.3.3 Screenshots should show the app in use, and not merely the title art, login page, or splash screen. They may also include text and image overlays (e.g. to demonstrate input mechanisms, such as an animated touch point or Apple Pencil) and show extended functionality on device, such as Touch Bar."
and
"2.3.7 ... Metadata such as app names, subtitles, screenshots, and previews should not include prices, terms, or descriptions that are not specific to the metadata type."
Did the rejection mention one or other of those?
I have normally used plain screenshots. Sometimes I have attempted to add explanatory text but that has often been rejected based on 2.3.7; I wouldn't try to do that again.