Windows Security - Virus & Threat Protection Disabled & will not Reactivate

Yeah, I have never rolled back to Windows 10 so I'm not sure if the errors of Windows 11 like what you're facing will come with it. I'm hoping Windows 11 DEV builds fix this Virus/Threat Protection issue soon. Only other thing I can think of is something damaged your files, maybe malware, and the malware is gone now but the damaged files are still there or gone but the damage is still present. Some would recommend clean installing Windows 10, but you can wait and see or wait into the stable version of Windows 11 arrives. You can also join the Preview Release Channel of Insider Program and you might be able to get the recent Windows 10 preview release that came out last week that maybe will fix the problem: https://techcommunity.microsoft.com/t5/windows-10/windows-10-version-21h2-announced/m-p/2554392