For the past several days at least, Google search results have not included AMP links on iOS 15, but they still include AMP links on iOS 14. I've determined that Safari's User-Agent makes the difference. (You can spoof the User-Agent on iOS using the Safari web inspector on macOS.) Here's my iPhone's User-Agent:
Mozilla/5.0 (iPhone; CPU iPhone OS 15_0_1 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/15.0 Mobile/15E148 Safari/604.1
With this User-Agent, there are no AMP links in Google search results, but if I simply change Version/15.0 to Version/14.0 and keep the rest the same, Google search results suddenly have AMP links again! This is reproducible on my iPhone, in the Xcode iPhone simulator, and also in desktop Safari Mac with its User-Agent spoofed as iPhone.
Why have Google search results changed? Why is Google checking for Safari on iOS 15? As far as I know, Google hasn't made a public statement, but I have a crackpot theory. One of the new features added in iOS 15 was Safari extensions, and one of most popular categories of Safari extensions is Google AMP blockers. My own Safari extension StopTheMadness blocks Google AMP (among many other features). Indeed, I discovered the change in Google search results while I was testing an update to my extension. So, is it possible that Google has given up on AMP in Safari on iOS 15 because of the popularity of AMP blocking extensions? Who can say, but it's certainly an interesting coincidence. I can say that it's a very recent change. I know from my own testing that Google search results still included AMP links for the first week after iOS 15 was released on September 20. Anyway, I invite others to reproduce my results, and to offer their own crackpot theories.
I've received a statement from Danny Sullivan, Google's public search liaison: "It's a bug specific to iOS 15 that we're working on. We expect it will be resolved soon."
So there you have it. My crackpot theory was totally wrong. Betteridge's law of headlines strikes again! But at least now we have the official explanation for the change.