The current situation
I just did a clean install of Windows 10 on my PC after upgrading the motherboard, CPU, and RAM. During the setup process, I entered my 25-digit product key for my full retail license of Windows 10 Pro (which was a free upgrade from my Windows 7 Pro). This was accepted with no issue. Once I got into Windows, I went to Settings -> Activation. There were three sections here at that point: Windows, Update product key, and Add a Microsoft account. I clicked the "Add an account" button in this section and signed in to my Microsoft account. Unfortunately, for some reason this does not appear to have linked my Microsoft account to my digital license. The current state of the Settings -> Activation page looks like this:
Edition: Windows 10 Pro
Activation: Windows is activated
Product ID: XXXXX-XXXXX-XXXXX-XXXXX (fully shown)
Product Key: XXXXX-XXXXX-XXXXX-XXXXX-XXXXX (last 5 digits shown)
Notably, Activation does NOT say "Windows is activated with a digital license linked to your Microsoft account." Also, the entire third section (Add a Microsoft account) has disappeared.
In Settings -> Your info, it shows my name, my Microsoft-associated email address, and that I'm an Administrator. So this is already a (connected) Microsoft account rather than a local account.
From the Activation page, clicking Get help results in a popup saying "Try again later - Something went wrong on our end. We're working on it." This has been the case for a couple hours.
In my Microsoft account (accessed via browser), under Devices, there is currently only one device listed: this desktop PC. The motherboard listed is correct (the new one), and it shows OS Edition Windows Professional, Version 2009, OS Build 10.0.19045.5555. This is my only PC, I only own one copy of Windows, and I only have one Microsoft account. Somehow the three of these aren't fully shaking hands.
How do I transfer my valid product key into a digital license? Do I need to reinstall my previous motherboard to do this? And how do I link my Microsoft account to that digital license?
Additional background that's probably unnecessary
I updated the hardware last week on 3/4, when I was running Windows 10 Professional N. The Windows 11 update downloaded and installed on shutdown that night, so I was in Windows 11 Professional N on bootup on 3/5. On Friday 3/7, I realized the "Activate Windows" watermark wasn't going to go away on its own, so I tried and failed to activate. After trying the various troubleshooting steps, I eventually contacted Microsoft help and received a phone call.
MS Help call 1
After I explained the situation, the help team representative had me do various things, some of which I'd done already and some of which were new. At the time of this call, I did not have either my Win 7 or my Win 10 product keys available. He suggested that I roll back to Windows 10, but Windows 11 had apparently automatically deleted the files necessary to do this. The rep said this was only possible after 10 days, but it had only been 2 or 3 days. I suspect the issue may have been that Win 11 installed one version but had already updated to another (23H2 to 24H2? I have a screenshot on a backup drive if this is important). The end result of this call is that he told me that people who upgrade motherboards are rare, indicating MS doesn't care about this market, and that my only option was to buy a copy of Windows 11.
MS Help calls 2 & 3
I pulled out a bin from my closet and found my original Windows 7 Pro disc and product key. I also searched an external hard drive and found my Windows 10 Pro product key. I contacted Help again, and this time the rep explained that the issue was that Windows 11 Pro N had installed. He felt that I needed help from another department to change my install to Windows 11 Pro (without the N) and that this would resolve the issue. Several hours later, I finally talked to someone in this other department. This person just told me that since I had changed the motherboard, I needed to buy a new copy of Windows 11. She literally hung up on me before I could explain 1) that I had a full retail license and not an OEM license, or 2) that another rep sent me her way to switch from 11 Pro N to 11 Pro. At some point after this call, I checked the Devices under my Microsoft account and saw that there were two devices listed. Both were desktop PCs with the same name, presumably my one desktop PC with the old and new motherboard. Looking at the details showed one had an unknown motherboard and was on Windows 10, and one had my new motherboard and Windows 11. I removed the Windows 10 device, hoping that this would allow my now-Windows 11 PC to activate. After a couple reboots and more troubleshooting, that didn't seem to have done anything.
Back to now
After that, I decided to just backup my important files and do a clean install of Windows 10 Pro (without the N) using the valid product key. And here I am.