If you use PS and LR extensively, consider 1TB option at least. 16GB of RAM on an iPad world can futureproof it for years after years.
Other than that, do you REALLY like to beta test mini-LED this year? If so, go for 12.9”, otherwise I think 11” is better value overall, and will break your bank less hard.
There is quite literally no difference from those two aside from size and weight of course. Willing to beta test mini-LED, go for 12.9”, not, go for 11”. However, if your workflow benefits hard from large screen and more viewing area, go for 12.9”.
To anyone else who is going to dislike my comment, I say that because there is literally no other device produced by Apple using mini-LED at the moment, hence the “first generation dilemma”.