I'm still trying to figure out the different versions of the .NET libraries.
Given an existing project, how do I know if it's using .NET Core or .NET Standard?
.Net Core and .Net Framework can use .Net Standard Libraries which is Shared Library for both.
The versions which is seen under drop down box is .Net Framework versions.
You cannot directly convert .Net Framework project using properties window. But, you can unload project and change TargetFramework to netcoreappx.x by editing .csproj file
If you are using .Net Core that screen you've attached would look like this:
You will need to download the .Net Core framework, available here: Download .Net Core
Then when you create a new app you select it to be a .Net Core application like so:
Good luck.
When you select the Application tab of unmodified project properties, whatever is selected in that drop down is the .NET framework your project is targeting...