Hmm, Hmmm. I kinda disagree. The area that is specifically screenshots is the "alt-picture" for people not wanting to read the description ;-)
Also here:
https://html.spec.whatwg.org/multipage/images.html#alt
the intent is that replacing every image with the text of its alt attribute does not change the meaning of the page
Alt is about meaning, not about descriptive transcription.
But as I see it, you have two ways of making it more accessible for those people using screen readers. Make a good description to begin with. And if you use pictures as a description, just place the alt text for those pictures in your description. There is html editor, is there not. You do not have to put your images in the screenshot area.
While screenshots are images (or even video snippets), the alt text would probably just read "screenshot". To be blunt, if the player can't see the screenshots, the player can't see the game either. And putting the information how accessible a game is for the visual impaired in screenshot form only, kinda defeats the purpose. So those games that are bound to have a good description to begin with, at least I would hope so.