Google no longer displays AMP labels or icons in mobile search results. I personally can no longer trigger it for any of my searches. No, it does not seem to be replaced by the page experience tag.
This is a screenshot of a page, usually with a gray AMP lightning bolt icon, but no longer:
This is a GIF showing a carousel of headlines without any AMP icons:
Last month, we saw non-AMP pages appearing in these areas, and now we even see that the AMP page (when you click on the result above, you will enter the AMP version) does not display the AMP label.
Others have also seen this:
It looks like Google has removed the AMP flash icon pic.twitter.com/Rurv2LEwqR
— Valentin Puletzer (@VorticonCmdr) July 20, 2021
Discussion in the forum Twitter.