[davesmith1983]

For the most part the situation is the same with .NET. Any code written in .NET 2.0 should work with 4.7.

The newer .NET Core most stuff is now compatible and it is pretty easy to write code that is compatible. Stuff that isn't compatible normally needs you to install a compat shim that Microsoft provides, but I've not needed them so far.

My major frustration is with the JS frameworks. I wrote some perfectly good Angular 4 code and I had to change quite a lot of it to work with newer versions of the framework.

[lukeschlather]

I haven't been working with .NET for very long, but my experience is that mixing .NET Core and .NET Framework leads frequently to very confusing, inscrutable error messages about incompatibility between the two. Though if it builds it works fine.

[davesmith1983]

The accepted method is convert projects to .NET standard and/or multi-target project itself. I haven't run into any issues but most of what I do is web projects, I wouldn't know if it was something like WPF.