Maths doesn't do Gods. Maths doesn't produce universes.
Exactly. Maths does do universes, though, and unlike claims of gods you can check the working.
Why does a created universe make free will impossible.
Because all of time exists as one; our subjective understanding is from moving point of reference in the dimension of time, but the entirety of the past and future are there, now. If this was created, it was created whole, and therefore it was created from the innumerable possible realities to be this exact one. All those perceived choices that are ours were preselected by a God that chose this iteration of reality to make rather than any of the others.
The important choice to accept or reject God is not about the universe.
You're absolutely correct, it's about the credibility - or lack of credibility - of the claim, when viewed against the available evidence.
O.