I found a possible workaround. Symptom: Multiple applications such as Pages, Notes, Preview print "UNIRAST" followed by garbage and many pages. Updating printer firmware and re-installing drivers did not help.
- Reset printer system
- Re-added the printer as AirPrint
- Then added it again, so it gives it the same name followed by "2", but this time I set it as Generic PCL Laser Printer.
So far, prints from Notes, Pages, Preview are going okay, as I've set this PCL version to my default. I found the idea here: https://discussions.apple.com/thread/250857812 where someone describes this same workaround, and also another useful link that didn't quite solve it was here: https://discussions.apple.com/thread/252484142 - there's a theory the drivers from HP aren't 64-bit, thus causing the problem, but I am not sure about that.