Accessibility API need a semantic layer that the DOM provide. You can't just make every arbitratry gui accessible. The app developers will have to pay the price (more development time).
I’m only familiar with Flutter which just happens to have a render to Canvas option on the web but they have a full accessibility tree that is designed for exactly that already with zero work from the developer.
Hopefully the GUI developers realize this is needed and put in the work, so that work can be shared by the end users of the GUI frameworks. I'd hate to think developers are going to reinvent the wheel on each project, but I've been less surprised before.
