Question: Are FSE themes accessible. Is the Site Editor accessible?
Answer: Accessibility is one of the Non Functional Requirements of WordPress, so it should be.
In the #fse-outreach-experiment testing calls the testers are asked if they were able to perform the task using keyboard only or screen reader. I recorded two sessions for call #5 where I attempted to complete the task using keyboard only. I did have some problems, for which issues have already been raised. It wasn’t particularly easy. I’ve been a mouse user for over 35 years; a keyboard user for 45. It didn’t help that most of the keyboard shortcuts didn’t work in the Site Editor.
I didn’t actually test the results displayed to an end user! So I’ll do that when I’ve saved this.