According to John Shehata, the Global VP of Audience Development Strategy & CRM at Conde Nast, Google is now testing not showing AMP pages in the Top Stories carousel in Google Search on mobile. Google can do this for COVID related news but outside of that, Google should be only showing AMP links in the Top Stories carousel.
John Shehata posted on Twitter saying "we are starting to notice some mobile queries producing non-AMP Top Stories carousels. We know that AMP will no longer be a perquisite to appear in Top Stories soon. Have you seen similar SERPs? BTW, some of the results are AMP but have no AMP icon."
Some of these sources to support AMP, but not only do they have no AMP icon, when you click on them, he said, it takes you to the non-AMP version.
I suspect that this is Google testing to prepare for the Google Page Experience Update where AMP will no longer be required for being in Top Stories. Note, the Page Experience Update will be launching in May 2021.
So Google testing this would not surprise me.
Forum discussion at Twitter.
