No. GTK3 has no support for accessibility API on Windows or macOS. Never had, and won’t get it in the future, as the toolkit is feature and API frozen.
GTK4 has a completely new accessibility API for widget and application developers; underneath it, it “speaks” the same protocol as GTK2, GTK3, Qt, and web browsers—i.e. AT-SPI.
There is currently no implementation for assistive technologies on non-Linux platforms, but the new API in GTK4 is designed to be portable from day 1.