Changing OS

Welcome to Apple Support Community.

You should not attempt to go back to an earlier version of macOS. Rather, follow these steps to fix your printer:

• First, delete all HP software and Apps.
• Next, Reset the printing system on your Mac to solve a problem - Apple Support.
• Finally, Add a printer to your printer list so you can use it on Mac - Apple Support.

Jack

+1, going back to fix a simple issue is not recommended.

1. In addition to the steps Jack offers the issue may be you are using outdate HP scanning software. In that case, first check with HP to see if they have updated their app. If they have not please go on to step 2.
2. Your computer has Image Capture pre-installed. Please begin using Image Capture. If you are not familiar with IC then please click Scan images in Image Capture on Mac - Apple Support. You can find Image Capture in Applications - Utlitilies - Image Capture or you can use Spotlight to launch it.
3. If HP does not have a more up-to-date version of their app and IC does not work, please try the trial version of Vuescan and if that works, please buy it. You can find Vuescan at www.hamrick.com.