Pretty much the first thing I tried to set up with I heard about Zellij and decided to give it a shot a while back was how to scroll back and copy paste text without using the mouse, since that's one of the core features of tmux for me. If my recollection is correct, the closest thing that I was able to figure out was some sort of built-in way to open output in a vim buffer, with the info I found when googling basically saying that it was intentionally not something the developers felt like it was important to implement anything closer to tmux for. Maybe it's changed since then but I distinctly got the impression that it using it would force me to adapt to a bunch of new workflows that didn't resemble anything I had seen before, and it didn't really seem worth the effort.