I won’t pretend that the Sourcehut accessibility situation ideal, but it’s usable for the most part with assistive technologies IME. From what I can tell, it doesn’t have critical issues like hidden/un-focusable items, interactive widgets that don’t change states, keyboard traps, etc. The only other forge that generally passes that is GitHub.
Core functionality all works, but ancillary functionality and quality-of-life could use some significant improvements. I’ll file some tickets later today; they’re generally easy to fix. Some that come to mind are using additional <nav> elements with different labels, and naming in-page heading anchors.
Edit: just saw your thread on Sourcehut accessiblity, I’ll take a look.