This was initially reported by developer Jeff Johnson where he had initially theorized that Google had applied a filter to suppress AMP links on iOS devices due to browser extensions designed to block AMP pages (some users actually don’t like AMP pages). However, it turns out that is not the case.
It's a bug specific to iOS 15 that we're working on. We expect it will be resolved soon.
— Danny Sullivan (@dannysullivan) October 6, 2021
According to a tweet by Google rep Danny Sullivan, he denies that is not what’s happening, but rather it is a bug specifically related to iOS 15 that is causing the problem. Sullivan notes that Google is aware of it and that a fix is in development and that it should be rectified soon. Since this fix is on Google’s end, there’s nothing for iOS users to do but wait for the fix which should be done server side.
We’re not sure when the fix will be coming, but based on the responses to Sullivan’s tweet, it seems that quite a number of users don’t really like AMP pages that much to begin with, so it doesn’t seem like many are eager to see this fixed anyway.