The major limitation is that macOS apps do not have to use the API and so there will always need to be a fallback to something like screen scraping for controls that don’t use it.

Zoom Desktop app is a prime example of this. Many of the windows (join a meeting, settings etc) are normal macOS ones, and those use AX buttons, but many are poorly / weirdly labeled (if at all).

But once the Zoom meeting appears, that’s all (?) custom, and so the best you can do is whatever Zoom decided to offer. The dreaded “this meeting is being recorded” pop up is a custom control and so doesn’t have AX at all; I have automation that basically looks for an appearing window and if it has “OK” just blindly click it and hope for the best.