Matthias Clasen has written a post on the GTK blog about recent changes in the accessibility implementation of the toolkit, as well as improvements in the tooling planned for the 4.12 release: https://blog.gtk.org/2023/06/21/evolving-accessibility/
It's important to note that more work is needed to improve the accessibility stack on Linux; if you want to contribute you can read the at-spi2-core developers documentation for an overview of the changes to the stack: https://gnome.pages.gitlab.gnome.org/at-spi2-core/devel-docs/index.html
We especially need more documentation on how ATs interpret the accessibility interfaces, and what kind of expectations should be satisfied by toolkits and apps.
@GTK I don't see any overview on this page though...
@emersion For an actual overview of the stack, the readme for at-spi2-core has a good outline with links: https://gitlab.gnome.org/GNOME/at-spi2-core/-/blob/main/README.md