Is there a way to see decompiled C# system libraries in VS Code?

Question

Thanks to this question, I can view Unity's classes:

Notice it says "Decompiled with ...". With classes which are part of system libraries, it doesnt do that:

Notice the lack of "Decompiled with ..." string. Indeed, it looks like just the headers.

Is there some extra setting to turn on somewhere to decompile ALL code, including system libraries?