"So just to confirm so I understand.
The Windows 10 Pro product key you have did not come from the free upgrade of Windows 7 to Windows 10?"
I'm fairly certain the Windows 10 Pro product key I'm using did come from the free upgrade of Windows 7 to Windows 10. I neither recall buying an additional retail copy of Windows, nor do I have any email records of a purchase.
"What I was pointing out was that if the Windows 10 licence you are using did originate from the free upgrade it would not be transferrable to new hardware.(motherboard) as the free upgrade period has ended and is now rigorously enforced."
The link you shared states, "Microsoft's free upgrade offer for Windows 10 / 11 ended July 29, 2016. The installation path to obtain the Windows 7 / 8 free upgrade is now removed as well. Upgrades to Windows 11 from Windows 10 are still free." My first thought is that their wording choice is terrible. Your interpretation of their wording makes sense, but anecdotally, I can search my email records and confirm that I bought a new motherboard in October of 2016. This is the motherboard I was using with Windows 10 until last week, reinforcing my take that retail copies of Windows can be transferred between motherboards (while OEM copies of Windows cannot). I believe I upgraded from 7 to 10 before the window of opportunity closed, and I'm currently trying to upgrade from 10 to 11 before the opportunity closes.
"When you upgrade to Windows 11 the product key (as a licence) should be converted to a digital licence as it was with Windows 7 or 8 to Windows 10.
There is no method to manually make it a digital licence in Windows 10 after a clean install if it doesn't show that already.
So in essence an original Windows 10 licence (that uses a product key) can always be used to activate Windows 11 while the free upgrade is still in operation. I just say that as I don't know if Microsoft may decide to end the free upgrade in the future."
Interesting. It seems that when I upgraded from 7 to 10, my product key wasn't converted to a digital license for some reason.
If the "Get help" button continues to give me the same error after I get Windows 10 updated as much as possible, I'll try updating to 11 and see if it works now that I'm on 10 Pro rather than 10 Pro N. I was hoping to sort out the digital license issue beforehand. Regardless, I'll report back. For reference, I was intending to do this through Windows Update, where it very clearly says the upgrade is free. (But maybe it's false advertisement due to something odd about my circumstances.)