If you `set-option mouse on`, tmux will let you use copy-mode just by clicking and dragging (intelligently within panes, negating the need to resize-pane -Z). But TBH I often do almost the same thing (but Xorg does its part of the copy-pasta without forcing any Emacs-esque three-finger keyboard chording, thank goodness), selecting text is the only thing I ever use the mouse for in the terminal (except rare scrolling, especially overflowed weechat bars), so I keep tmux’s mouse support off.