Q:

Is this grammar valid: I have no idea what you need to make it work on a Mac

This statement here: 
I have no idea what you need to make it work on a Mac. 
seems off to me regarding grammar. Is it not supported to be why instead of what?

A:

It depends on the context, which you have not provided. 
If you are questioning the necessity of making something work on a Mac, then it should be written: I have no idea why you need to make it work on a Mac. 
If you are questioning what tools or methods are required to make something work on a Mac, then it should be written: I have no idea what you need to make it work on a Mac.

