iOS users do not see "Login with Google" option even though OAuth2 via Google is enabled

See subject. A new discourse 2.7.0beta instance, I turned on Google OAuth2 and set it up.
It works fine for Android users (and web users), but iOS users report that the “Google” button is not offered on sign-in. Is this expected?

PS: now the user reports that on a subsequent visit, they are offered the button to log in with Google after all. Note that I didn’t publish the URL until after I had Google OAuth2 enabled, so caching should not have been an issue.

In other words, it doesn’t appear to be reproducible, but the user was able to produce a screenshot that clearly showed the respective button absent.

I like to blame anything I don’t understand on caching, so maybe it was some sort of proxy caching between your server and the browser? As it happens, I didn’t notice this problem on iOS when adding this feature.

All’s well that ends well.

We are now suspecting an interaction with iOS’s intelligent tracking prevention feature which this user has activated and others (for whom this didn’t happen) did not. Apparently, this feature is known to cause interference with Google’s SSO. See here. Although I haven’t been able to find a source that also experienced this particular failure where the button didn’t appear. I haven’t checked the JS logic for it. Could there be an interaction with tracking prevention (which automatically removes cookies unless the user interacts)?