No. Those are examples of portability issues when your application depends on platform specific functionality:

Most code containing P/Invoke calls into native Windows Libraries (as opposed to P/Invokes done to your own C libraries) will need to be adapted to the equivalent call in Linux, or the code will have to be refactored to use a different call. <-- Means when you choose to directly link to Windows technology.

Registry <-- If you choose to use it. I haven't written any registry dependent code for the last ten years and don't even miss anything about it.

you should not assume the order of bytes <-- Not .Net's problem.

... the list goes on.