how to report them if not.
Do not bother. The disclosure feature is only mandatory for assets. It says so in the OP. The plan is to delist all assets that have not filled out the disclosure. I have no clue how long that grace period is supposed to be. There are still about 20k assets without that info. After that grace period, you would just browse with the no-ai tag to avoid ai. But that's assets.
is there a way to tell from a store page
Maybe one day. When that grace period is over, they might complete the feature. It is rather crude to introduce a tag that is not a tag, but can be searched with the tag system - and is not even visible on the page. All the tags you see regarding ai, are manual tags. You cannot see the disclosure tags in the info box.
The only way to check, is to combine the tags of the game with one of the ai tags and see, if it appears.
Only about 20% of the games on Itch have filled out the disclosure question.
In my opinion those tags are not all that helpful for games. I would prefer an extensive and visible disclosure as is seen on Steam. If you just browse with ai-generated, you do not know, how ai was used. People that want to avoid ai, usually want to avoid ai "art". Sure, there are some purists that want to avoid all things that have anything to do with ai. While browsing on a browser that has ai assisted code in it, that would be marked as ai-generated on Itch. Speaking of, the Itch app is chromium based, is it not. So the Itch app itself would be marked as ai-generated.