Malware message when trying to print to my HP Deskjet

Perhaps, but there are well over 100 different HP DeskJet models and you need to determine which one you are using.

• If it is an AirPrint-enabled device no manufacturer-provided software or drivers are necessary, and the affected files can simply be deleted. See below.
• If it is not an AirPrint-enabled device you will need to wait until HP fixes the problem they caused by revoking the security certificates for their software. Check Software Update: How to update the software on your Mac - Apple Support. If HP has not fixed it by now, check Software Update some other time. Repeat tomorrow, next week, or as often as necessary until you eventually decide to give up on HP and buy a printer / scanner / MFD from a company that actually knows what they're doing.

Otherwise please contact HP or peruse their community help site, which recently become overwhelmed with reports substantially identical to yours: HP Printer Setup, Software & Drivers.

Apple recommends that you do not install any software that came with the device or from the manufacturer's website. If you did, remove that software, and then add the printer to Printers & Scanners again as AirPrint-enabled device. The existing device entry can and should then be removed.

As of this writing there are well over 6000 AirPrint-enabled printers and multifunction devices. Over 1000 of them are HP devices. I don't recommend any of them.

You might want to peruse this page as well…

If your HP printer doesn't work and you see a warning that HP software '...will damage your computer' - Apple Support

For routine home / home office use I favor Brother printers these days. No complaints, unlike the HP printers I have had in the past.

They are very reasonably priced and consumables aren't outrageous either.

Any AirPrint-enabled printer will do though.

👍