I use screen still too, partly because it’s generally installed on everything already, like vim. I hardly ever use anything but a maximised (i.e. full-terminal) screen at once, so it doesn’t sound like I’m missing much from tmux.
De/reattaching’s extremely useful and another thing I really like in screen is being able to scroll and search the scrollbuffer.
If I was ready for an upgrade, I’d probably go for zellij.