Headline would be more accurate without the Copilot PC part; that was just one of the ads.
Anyway, here's the countermeasure I use to prevent Win10's obnoxious fullscreen upgrade-to-11 ads.
It's one line. Run in admin cmd. Result will be Success if the task exists or an error it couldn't find it.
schtasks.exe /change /tn "\Microsoft\Windows\WindowsUpdate\RUXIM\PLUGScheduler" /disable