How to enable "Scan Items from HP Devices"

OK, here is what I did that seems to solve the problem.

Problem: Scan to Computer from the control panel of HP MFP does not work. A process begins to run on the chosen computer but ends with either the error message, This workflow contains "Scan Items from HP Devices", which is provided by a third party. Third-party actions must be explicitly enabled, or, if third-party actions have been enabled, Scan failed. The action "Scan Items from HP Devices" encountered an error: "NSWindow drag regions should only be invalidated on the Main Thread".

Remark: Third-party actions can be enabled in Automator. Run Automator from the Applications folder, click its name in the System menu bar, select "Third-Party Automator Actions..." from the drop-down list and follow through. Some Adobe apps require third-party apps to be enabled, so it is possible that that has already been done by another person and/or on another occasion, and with respect to the problem at hand, the first message never appears, only the second.

Solution: The following is an adaptation of ShlomiL's advice (https://h30434.www3.hp.com/t5/Scanning-Faxing-and-Copying/Cannot-initiate-scan-from-OJ-x476dw-to-MacBook-Pro-Touch-Bar/m-p/7251404/Pop_SU#M214267). I describe exactly only what I did that worked and omit his/her recommendations in case something does not work. I did not try anything that did not work.

1. Download HP Easy Scan from http://ftp.hp.com/pub/softlib/software12/HP_Quick_Start/osx/Installations/Essentials/hp-easy-scan-1_9_2.pkg and install it. It will be installed in the Applications folder, but not in any folders that might exist there containing other HP printer/scanner apps, e. g., not in one labeled "Hewlett Packard" (my case) or "HP" (explanation for this case below).
2. Check that the app works by executing it and making a test scan.  Remark: I cannot make a recommendation for the case that it does not, since it worked for me. In that case, it would probably be best to follow ShlomiL's recommendation.
3. Ensure in HP Utility | Scan to Computer that Scan to Computer is enabled. Remark: I recalled seeing an alias to this app in the "Hewlett Packard" folder in Applications; however I could no longer find such a folder there. Instead, there was one called "HP" that contained, inter alia, everything that used to be in "Hewlett Packard" plus a second alias to HP Utility.
4. Check that Scan to Computer now works from the MFP. Remark: If not, see my remark for step 2.
5. Clean up.
   1. Trash the old HP Scan app in the "HP" folder in Applications and empty Trash. Remark: It would be prudent to ensure that Time Machine has previously backed it up; however, scanning, whether initiated at the MFP control panel or on the Mac, seemed unaffected in my case.
   2. Move HP Easy Scan into the "HP" folder. Remark: Except for having to remember the new location of the app, this bit of tidiness seemed to have no adverse effect on scanning.

Remark:  I looked into the HP Easy Scan.app contents.  It seems not to address the problems to which the error messages above pertain, perhaps it does not even use Automator actions (see https://www.computerworld.com/article/3142666/does-apple-really-want-to-kill-automator-applescript.html).  I am not sure I would recommend replacing HP Scan by HP Easy Scan on, say, a machine running macOS 10.13 that is not exhibiting some ambivalence towards Scan to Computer.

Discovered how to explicitly enable third-party action:

1. Run Automator
2. Click on "Automator" in the menu bar
3. Click on "Third-Party Automator Actions..." in the drop-down

Now, when I attempt to initiate a scan from the control panel of the MFP I get the error message:

The action "Scan Items from HP Devices" encountered an error:

"NSWindow drag regions should only be invalidated on the Main Thread."

I've hunted around in the HP Support forums. No solution there, just suggestions that desperate users try only to create more problems. Anybody have any ideas about this error?

Very important addendum to solution: If you enabled third-party Automator actions to solve the problem about which the first error message above complains, remember to disable them!