Botched up Windows Update has broken my Windows 10 (June 2021)
[I'm aware this is not what he asked - considering the issue it still may be the best approach.]
This may not be what you're hoping to hear, but as I'm dealing daily with those issues, the best advice you can and will get is the following:
- Backup your data
- Make sure your drives are still healthy (run disk checks, etc. from a bootable USB [Linux Live System] - there are tons of guides available - currently on mobile though)
- Swap your hard drives if needed
- Follow up with a clean install of Windows
Why is this the best solution (From experience as a SysEngineer with 10k Windows nodes in my previous/current job):
The chances of getting your installation fully working again without tripping over countless other issues is very, very slim. Those issues may occur directly or after weeks/months and may keep piling up to the point of no return regardless of your measures. Additionally you'll benefit from a fresh and clean environment and you'll get rid of tons of no longer needed files/folders. Windows Updates - especially feature updates as f.e. 21H2 are known to cause issues of that scale and nature.
In the end it's up to you if you wanna continue troubleshooting, but if you don't wanna invest countless hours holding on to a glimpse of hope, I strongly suggest the method mentioned. ;)