Printing warning: “hpPostScriptPDE.plugin” will damage your computer
I had the same problem after updating to Catalina 10.15.7 on my older Mac Mini. To fix the printing warning (and allow printing) I first deleted the HP drivers and then installed new ones. My HP Color LaserJet 2025 wasn’t one of the options with the new drivers but the OS selected Laserjet CP2020 and it seems to work fine. If nothing comes up that looks close to your printer, you could try “generic laser printer”.
You can download the uninstaller at HPs site:
https://support.hp.com/us-en/document/c06960563
I found the new drivers on Apple’s site:
https://support.apple.com/kb/DL1888?locale=en_US
My Mac is too old to install Big Sur and My wifes’s doesn’t have enough space so I can’t test it with Big Sur.
I don’t think it is a problem with HPs certificates as Allan said since the same printer works fine on my laptop running 10.6.8.