Doesn't matter if some specific language lacks recursion. UG refers to a capacity of the human mind: if it happens to be the case that there is some language which does not feature recursion, that does not show that humans do not have that capacity. Just like how if there was a person somewhere who had grown up in isolation and never learned a language wouldn't show anything about UG.

But don't you see how you've just made the hypothesis unfalsifiable?

Do you also think the claims that dogs can talk or that humans can fly are unfalsifiable?

All we are discussing is a biological system, and biological systems are things that may be investigated.