When a number of things go wrong from an error as happened here, the best thing to do is a Windows 10 Repair Install. There are 3 ways to proceed:
Keep Everything - best if it works and your computer comes back just the way you had set it up except repaired.
Keep Data - necessary if the operating system damage is extensive. Keeps the User Profile and makes software install quite easy.
Keep Nothing - deletes the User Profile and all else and is essentially a fresh install. Necessary if the User Profile is damage. Be sure you have backed up all your data.
https://www.microsoft.com/en-us/software-download/windows10
Windows 10 is running, so click on the Download button (not Upgrade
Button) and select Run. If the Repair will not run as per above, use
the Download button to create a USB Windows Installation key, then run
Setup on the USB Key.
This will launch the Repair and proceed normally.
Start with the option to Keep Everything.
You can also Keep Data, or Keep Nothing. Keep Nothing is very close to
a clean install.
%WinDir%\System32\config\RegBack, you'll need to do a repair install as covered in @john's answer. You can tryDISM&SFC, however due to the system hives being fluid, it's not likely they would correct the issue – JW0914 Feb 18 '21 at 14:31%WinDir%\System32\config\RegBack(user's hive is stored in%UserProfile%) and re-enabling the backups via the Registry isn't 100% reliable; however, the program ERUNT can create Registry hive backups and be scheduled to do so at specific intervals. Due to ERUNT's site lacking HTTPS for the download, it's recommended to download it from a trusted third-party, such as BleepingComputer. – JW0914 Feb 19 '21 at 16:20