Thank you very much Jan.
Went to the Apple Support page - Looks like Apple has unintentionally revoked older HP drivers certificates. My HP Laserjet 1012 is not AirPrint capable. So I followed the link to HP support.
They tell you to uninstall the drivers, then reinstall. But when you go looking for drivers for the 1012...there are none! HP Printer Driver v5.1 doesn't open in Big Sur.
I'm scared to try Gutenprint driver - its unsupported in Catalina and feel less confident it will work in Big Sur.
I tried to get a driver for another model but it tells you to download HP Printer Driver v5.1 that doesn't work.
Looks like it may be the end of the line for my wonderful Laserjet 1012. It's given me 15 year of wonderful, uninterrupted service! :( Will have to keep a Catalina running MBP around just to have the ability to print. Shame.