I would have preferred taking AP stats/physics/CS/Calculus with a computer, and that was over a decade ago. (AP French also used
cassette tapes to record yourself with. Looks like they transitioned to the modern digital age in 2017, but I'm sure every year before then they had a sizable number of students with blank tape or broken tape submissions.)
I had already taught myself the basic TeX for math formulas before I took any AP test that could have used it, I even set up a PHP portal to do simple chemical equation balancing that would use LaTeX behind the scenes and spit out PNGs. There are nice JS libraries to do everything client-side now, so in any online portal it could be seamlessly mixed in with a reference and live-preview right next to it. All I'm saying is it's really not hard -- you can learn what you need in under an hour -- and if you step back and think about the type of student taking these tests they're also the type of student likely to pursue these subjects in college, so they're likely going to have to learn much more of LaTeX eventually anyway.
Where neither plain text nor LaTeX help much is when you really need to draw something out. I'd say mouse drawings are better than nothing, but you can also just remove questions/scoring that rely on display of such. Nothing stops a student from drawing privately on their own paper -- indeed as I recall a lot of the questions from some of those AP tests were exactly like that: do your work on paper you throw out after, because the answer is multiple choice.
It's really most surprising that they didn't go with a fully online test (which means no manual submission of purely offline artifacts) and haven't been preparing for such at all over the years...