Interesting, though I am citing the AMP spec, and it does say MUST. I'm curious if Google would put a self-hosted AMP page, for example, in their carousel. I think it probably can't.
>Besides algorithm changes, there will be several user-facing changes. For starters, the Top Stories carousel in Search will no longer be limited to AMP content. The Google News website and mobile apps will similarly surface more non-AMP content. Lastly, the AMP lightning bolt icon will no longer be used to badge eligible content:
https://9to5google.com/2021/04/19/google-search-page-experie...