alt Hacker NewsData point of one: in my small community group that has moved to Zulip we do have a grandma contributing. No jocks though so I can't speak to that.
I would also like to note that Slack did not pass the grandma test in our case. I highly doubt that Discord would given how hyperactive the UI is.
As a software engineer who's had to interact with Discord only a handful of times, I had no idea when other people could hear me or where I had to click to find people I was looking for.