This is currently not working in iOS 15. See: https://developer.apple.com/forums/thread/691021

I can also confirm. The magnifier (touch callout) is presented even when there is no text which can be selected, so this definitely seems to be a bug in safari. The only thing that seems to prevent this is calling event.preventDefault on touchstart. However, this isn't a viable solution since that also disabled scrolling, but it may be a workaround in some cases where scrolling isn't needed.