什么 is a word that can be used before a noun or by itself to indicate who or what. But it has a special use when it appears in this formula.
Formula of 什么~不~
什么+ verb/adjective/noun 不 verb/adjective/noun = No matter…/I don’t care…/It doesn’t matter …/It has nothing to do with…
Here is a dialogue:
A. 这门课好难啊！This subject is very difficult!
B. 什么难不难的，我一定会学好的。 No matter how hard it is, I make sure to learn it well.
More examples:
什么谢不谢，都是一家人。Don’t mention thanks. We are all a family.
什么山区不山区，去哪儿都行。It doesn’t matter whether it is a mountain or not, I can go anywhere.
什么通过不通过，他才不在乎呢。He doesn’t give a shit whether they approve of him or not.