On the hamburger menu there’s a [Users] choice. If you tap that you’ll get a roster of users active in the last week. Which you can sort by post count to see the busy ones. You can learn a surprising amount of stuff fiddling w the scoping & sorting options on that page.
What’s amazing to me is some of the most vociferous posters are folks whose posts I almost never see. Why? Different categories mostly.
ETA: That display is vastly more readable as a table on a tablet or larger screen vs near useless as a list of fact-boxes on a phone.