Why cant I run Tests within Visual Studio 2019 Pro and 2022 Community, .Net 6 of 5, on a UAP 10.0.16299

Question

I get a compatibility error: "Project PrimitiveDataTypes is not compatible with netcoreapp3.1 (.NETCoreApp,Version=v3.1). Project PrimitiveDataTypes supports: the project requires an SDK uap10.0.16299 (UAP,Version=v10.0.16299)"

The error showcases when I Add a Reference from my Test Project to the Project I seek to test in my apparently outdated Application. When that happens, I am also unable to download any NuGet Packages needed for the process.

I changed the Target Target Version of the old Application to an upgrade, a Version between 2.0 upward, and the error message reflects the change or the project will not reload. It takes me in circles as I search for a solution.

Steps I took so far is just about everything I found on Stackflow, Microsoft, and other familiar information sources.

I tried to upload the Project but was unsuccessful.

I am appreciate your help.