This morning I allowed a general NuGet update of my Win App SDK project. Once I cleaned out obj and bin folders I ran a full solution rebuild and it failed with the error:

"A referenced assembly was compiled using a newer version of Microsoft.Windows.SDK.NET.dll. Please update to a newer .NET SDK in order to reference this assembly."

Fortunately I had a full backup so I was able to progressively re-apply NuGet updates at an individual level and found that Microsoft.Graphics.Win2D was the component that caused the error. NB As part of my diagnostic I did run the latest Visual Studio update to 17.7.4 and tried rebuilding again, with no joy.