How do you translate “It is what it is” into Latin?

A non-trivial one. The meaning needs to be captured, and the meaning is that “it is no more than what it already is; we are stuck with it.” Which means I’d rather render the second is as ‘become’, ‘end up’.

Est sicut factum est “it is as it has become” is a start.

Ut fit sic sit “as it becomes, so let it be” is catchier, though perhaps it goes in a different direction (“if it ain’t broke don’t fix it”).

Est id, quidquid fit “Whatever it is becoming, it’s that” is maybe a bit closer.