I've just set these 'switches' in my Registry, as the update keeps downloading and insists installing Windows 11. That is even after having an on-line chat with a Micro$oft person, who provided an additional resourse:
https://www.yourwindowsguide.com/2021/12/block-windows-11-update.html#.YfUonPinzws
I shall provide a reply to this post if any further update process attempts skullduggery!
Martin.
The registry switch *on its own* only works *before* the Windows 11 update appears.
If Windows Update has started downloading Windows 11, it is too late.
By then it has created the download directory for the Windows 11 upgrade.
The directory name (29915d28b757d79214ddd971f3fd6134 on my machines) is an identifier.
The identifier tells Windows Update (wuauserv) that it has a patch that isn't finished downloading yet. So if Windows Update is running and finds the directory, it will proceed with downloading the corresponding files from Microsoft.
And if you delete the directory, while wuauserv and bits are running, the services 'know what they are working on', and will recreate the directory immediately.
So.. Stop wuauserv and bits. You need admin privileges to do this.
Delete the directory.
Reboot.
If you have entered the registry keys correctly, you should now be targeting Windows 10 21H2 instead of Windows 11.
Full instructions in earlier posts. Will not retype them.