As I understand, itch.io allows you to upload comics and other stuff that isn't directly a video game. But how much of a degree does it allow that? If I wanted to make a sprite or ascii movie in javascript or some other means of distributing it such as downloading an mp4/ogg, would that be allowed? I know this isn't youtube, but I was curious and wanted to know if animated movies (Such as sprite or ASCII or anything like that) were allowed on itch.io.

Yes, probably. That's what the "everything else" category is for. Not sure if people come to itch.io for that sort of thing, but you can try.