> the vast majority of Reddit's userbase is on new Reddit on desktop and the official app on mobile

I think this is probably true, but has Reddit published any metrics to confirm this?

I'd be especially interested to see the usage patterns segmented by contributors vs. lurkers. I'm sure it's true that the majority of Reddit users use the official app and new reddit. But I'm far less certain that's true for the majority of users who post content to reddit, or who moderate large communities.