My understanding is that AccessKit is an entirely separate thing to the portal.
Unfortunately, for several things, your choices are X, which is broken by design and few developers QA their software for anymore, or Wayland, which works pretty well in many areas, but where several important (or even basic) features are quagmired by bike shedding. But things are improving really quickly, and part of that is everyone shifting focus to Wayland.
I recently tried to navigate my GNOME desktop via screen reader and did not enjoy the experience. If I ever need it, I hope it works properly by that point…
At least for me, X is a worse experience on every computer I own (including the NVIDIA one), which is why I use Wayland. Neither is problem-free. I’m fortunate enough not to depend on accessibility features; perhaps my opinion would be different then.