I've seen this question! from 2 years ago:
Given $F$ is a $PRF$, we define $G$ for an input $x\in\{0,1\}^n$ as follows:
$$G(x) = F_k(x) \oplus F_k(x \oplus 1^s)$$
The question was if $G$ is a $PRG$. I edited the question a bit to fit the answers given back then. The answers stated this isn't a $PRG$ because $$G(x\oplus 1^n)=F_k(x\oplus 1^n)\oplus F_k(x\oplus 1^n \oplus 1^n)=F_k(x\oplus 1^n)\oplus F_k(x)=G(x)$$Now because $x$, the seed, must be random and because the adversary cannot affect the seed in any way. Why wouldn't this be a $PRG$?
For a random uniformly selected $x$ shouldn't the output of $F_k$ on input $x$ and $x\oplus 1^n$ be pseudorandom and thus $F_k(x) \oplus F_k(x \oplus 1^s)$ is also pseudorandom?