Windows Server 2016 to 2019 Upgrade failure diagnostics

I am trying to go through a Windows Server 2016 to 2019 upgrade in a test VM. Please don't give me don't do this feedback. That isn't helpful and I want to learn how to fix an upgrade. This should be possible.

The server is a fully patched desktop experience VM. I've tried all sorts of various but an upgrade always fails. I've even uninstalled the server on it. It still fails and the why is eluding me.

In the Windows 10 desktop world setupdiag.exe used to help translate the cryptic and verbose logs into something you could actually resolve in terms of an issue preventing an upgrade. Most of the online guides skip failure altogether or suggest contacting Microsoft support which isn't helpful. Can someone point me to a useful tool or guide to figuring out what actually is preventing a Standard Windows Server 2016 to 2019 upgrade?

The logs are cryptic as heck. The product seems to be unable to set a valid product key.
Setting product key failed. Error: 0x80070490[gle=0x0000007a]
I used a new valid MSDN Server 2019 key and a matching ISO for the upgrade.