I just ran into the same issue with my Dell XPS Core i5 mini-laptop. It's eligible for the Windows 11 upgrade, but I prefer to stay with Windows 10 for as long as possible.
The solution, in my case, was to make sure there were no pending updates. Sure enough, there were, and downloading, installing and restarting fixed the problem! My laptop is now covered for another year. It's the most basic step, and something I would've suggested back when I was a Microsoft PSS employee (wish I still were, I miss being a part of Microsoft).
For anyone reading this in future, follow these simply steps:
- Click on the 'Start' button, choose "Settings" (gear icon)
- Look for "Update & Security" and select it
- Under 'Windows Update', look for any pending update(s) listed
- Click on "Download" on each update (particularly the October cumulative update!)
- Wait and allow it to automatically download and install each (make sure you're connected!)
- Restart Windows 10
- Try re-adding your device for Extended Security Updates, it should work (if you meet qualifications)
On a side note, I've just noticed after applying the ESU it's claiming my laptop now does not meet the minimum system requirements for Windows 11 (odd, this wasn't the case earlier). Were the qualifications broadened in the last few weeks? Regardless, don't let this deter you from getting extended support, it is highly recommended if you want to keep your system secure.
Hopefully this works for most people (again, it's a very basic step, but one often overlooked).