We couldn’t complete the updates. Undoing changes. Don’t turn off your computer.

No luck. A long time downloading and installing 21H2, and on the second reboot, 'could not install' and 'undoing changes'.

KB5007186 was the last update successfully (and automatically) installed on November 15.

After seven months of this thread, does anyone know if Microsoft actually has any information on this problem?

Try this:

manually update to the very latest Windows 10 version (directly to version 21H2)

^For me that issue didn't came. I pressed that button and patiently waited. Now I have 21H2 on my machine.

Perhaps do it exactly like I did: try to install 21H2 not from your normal Windows user account but from what is known as the built-in Administrator account. If you guys are using "pro" version of windows then this Administrator account already exists and is visible and listed among the users and all you have to do is login. But if it is the "Home" version of Windows you have (very likely the case if your current window came pre-installed when you privately bought your machine for personal use) then in that case this built-in Administrator account is dormant and not turned on by default and therefore not visible in your list of users. But it is there. You just have to first turn that on in settings/control panel or via powershell (unless you are like me and have that thing already turned on and available at some point previously, from which is where I just updated my machine into 21H2, and not from my normal day to day user account (never mind that this user account also has administrator privileges, don't forget this is the strange quirky world of Microsoft). And careful I'm not talking about creating a new account and naming it "Administrator" but rather activating an account that is already there hidden and disabled in your pc and already has "Administrator" as username, which is why it's referred to as "built in". It used to be not hidden in Windows 7 but I digress. Once you have fired that up, login to it and from there try to go to the microsoft.com link and try manually updating your machine to version 21H2 then after that's finished go back to login with your normal user account. See if that works for you guys. Just one more trick you could try. We have to help each other cos Microsoft has abandoned us and "left us to our own devices" as the expression goes.... except in our case it's not an expression but literal.

After months of trying to update through Windows 10 Updater..and always failing, I successfully updated to 21H2 by going directly to Microsoft's web-site and entering "Windows 10 21H2 Download" . I downloaded the file and installed. It took nearly 1 hour of the computer automatically rebooting, but finally everything updated.