Windows 10: Windows 10 Antivirus Engine Unavailable and all attempts to remedy have failed

I have a laptop with Windows 10 and it is impossible to start Defender or update it because the engine is unavailable. I have used the McAfee and Malwarebytes removal tools, downloaded and installed as Administrator the Windows Defender app from the Microsoft site no error messages but nothing seems to happen and made various registry changes suggested in this forum. The internet is awash with posts about the Windows antivirus engine being unavailable so I doubt that the cause of my problem is unique and I would have expected MIcrosoft to have developed a simple, straightforward way to recti

:)

 

Windows defender-not updating-Engine unavailable

@Try3

Thank you for your quick response. You have always been quick to respond.

This morning I updated the HP laptop to 21H2 through the normal Windows update. Do you still think I should do a repair install with 21H2 ISO?

I am posting three screenshots .













I am yet to try the suggestion made by @hdmi in his post #8

"See also options 2 and 3 in this tutorial:
Windows Defender not updating automatically in Windows 11/10"

I shall try it later tonight and report to hdmi. He must be waiting in the wings.

 

Windows defender-not updating-Engine unavailable

He has not been doing a Repair install ever since post #2 so he is unlikely to bother now.
#2
#5
#7
#15
#26
#33
and now #36


All the best,
Denis

 

Windows defender-not updating-Engine unavailable

Option 2: Run the Windows update trouble shooter : Trouleshooter couldn't identify the problem.
The report:





Option 3: Trigger Microsoft Defender using Command line: Failed





When I closely looked at the Security Intelligence updates I observed that the update was downloaded, While installing it the progress indicator jumped from 0 to 33% , remained there for sometime and then jumped to 66% remained at it for sometime and then jumped to 100% but before you can even see it, the the error message pops in.. So I believe the install was also complete but it did not find the engine to attach to, Engine unavailable.
The error message:





Sometimes it is 0x80070643 and sometimes it 0x 80070005.