It's like so many other projects we're talking about here: it has sane defaults. If you start Zellij for the first time, it shows you menus to do all the things you might want. A big plus is that it supports mouse scrolling by default, and the scrolling works 100% of the time as far as I can tell.

I don't know if it can do everything that tmux or screen can do. I bet it probably can't. But it does all the things I want such a thing to do, and without needing any configuration on my part.