one way function xor with its input


I have the following question: enter image description here

I saw the question here What will i obtain if i apply a xor-ing a one way function and it's input? but from what i understand its only when f(x) is not length preserving, correct me if i’m wrong.

I think its not one way function but I cant build a function that invert it without inverting f(x), can anyone show me how it can be done?

thank you