What are the accessibility features that online spaces should have but often lack?

Online communities can be hugely beneficial for people that often face barriers to socialising or contributing to offline communities. I've seen in some recent discussions that a lot of community platforms don't do enough for people with disabilities.

So, I'm curious about what features platforms could/should implement, to make sure that as many people can have their voices heard as possible.

I'll start:

Alt-text on images that allow the visually impaired to hear what the image shows.