I started doing accessibility at GitHub when it had a flat structure (2013) and no one was telling me what to do. In my free time I will just browse the issue backlog and find things I could do. Eventually, I found that there are tons of accessibility issues that are just stale, and a lot of them were just like: this icon button isn’t labeled. I looked at them and thought oh that’s easy. I will fix it.
At one point I added so many aria-labels that AT users got mad that they’re getting misused.