Big Sur killed HP LaserJet 3600

I was surprised several months ago when I connected my mom's HP LaserJet 3600 to my MacBook Pro (running Catalina) via USB (with USB-C to USB adapter) and the printer worked! In fact - the printer worked amazingly well.

Then along comes Big Sur... and as soon as I connect the printer, I get the attached warning regarding "will damage your computer". Wading through HP's web site - they suggested running their uninstaller app... so I did. Well, that removed all HP drivers including for another printer that still works fine...). So I have the other working, but there are NO drivers for this printer, not even legacy drivers... I'm stumped. I really would like to use this printer - and since it worked just fine under Catalina... I do not see a reason for it not to work under Big Sur (other printer drivers are working fine).