Hi, I’m having the same issue, I got around it this way:- press “print” as would normally do, when the box comes up showing printer not selected, just press print in the top right corner, this then brings up another box, scroll down to “hp smart”, then a print preview will come up, press print at bottom of screen, an error shows about paper size, just press ok, then print again. You need the hp smart app on your phone for this to work. I hope this helps. I bought my first ever hp printer today, this issue is frustrating but it’s definitely to do with iOS 15, as my partners iPhone 12 is on iOS 14 and works perfectly using AirPrint with our new hp printer. Apple need to sort this issue urgently.