How to debug XF source code?

[FoggyFinder]

This is basically the same Q as #11085
Clearly the instructions Debugging Xamarin Open Source Frameworks: Part 1 – Xamarin.Forms is outdated.

I can build Xamarin.Forms.Core and some related projects (not all of them though) without errors but I can't debug them on a test app with direct ProjectReference. App stops on breakpoint but ST is gray and I can't walk through it.

Since I can't create nuget package I tried to copy .dlls manually into "bin" folder. After that I was able to debug Xamarin.Forms.Platform.Android project but not Xamarin.Forms.Core one.

Any suggestions are welcome.