There are a lot of good ideas in here!
For me, I do short video updates of the progress made after working on my comic weekly on my Patreon page.
I also, on occasion, do short stories based on folks (usually couples) that exist in the world of my comic, but that isn't related to the main story (since I can't just make a side character and leave them in the background lol).
QnA after each chapter of my comic, natch.
I also have a blog where I sometimes talk about experiences with making art and comics, inspo, and processes.
One thing I've been contemplating is sharing snippets of my codex, but I don't think many folks would be interested in that, alone so I would have to pair it with art to make the info into an infographic. I'm mad verbose and my codex is a full binder's worth of notes and info and I have a physical and digital copy of, and that's not including notes on fashion XD.