There is a new manuscript on the arXiv by Giulio Bresciani, _A higher dimensional Hilbert irreducibility theorem_, arXiv:[2101.01090](https://arxiv.org/abs/2101.01090), which shows that assuming the weak Bombieri--Lang conjecture, there cannot be a polynomial bijection from $\mathbb{Q} \times \mathbb{Q} \to \mathbb{Q}$. 

The author writes that: 

>Our strategy is essentially the one followed in a "polymath project"
led by T. Tao, see [Tao19], hence this result should be credited to the polymath project as a whole.

[Tao19] https://terrytao.wordpress.com/2019/06/08/ruling-out-polynomial-bijections-over-the-rationals-via-bombieri-lang/