I was quite satisfied with tmux but this issue (and one other) really drove me to seek an alternative like zellij so bad, but just couldn't settle on it for one reason or another. Instead I ultimately found refuge in kitty term which as a whole emulator is an overkill, but it's a great replacement and mostly as customizable. It does a good job with windowing - I particularly like the xmonad style window size switching. But there are still some parts of the tmux ecosystem I miss, like tmuxinator and the extracto plugin but otherwise most of my needs have been met, and the speed is a welcome bonus. So, can definitely recommend kitty as a good tmux alternative.