Switch to pane to the direction
panes
// what it does
Ctrl+b followed by an arrow key runs select-pane -U/-D/-L/-R, moving focus to the pane in that geometric direction. tmux picks the adjacent pane by on-screen position, so Up goes to the pane physically above the current one. This is the most intuitive way to hop between splits.
// shortcut
Ctrl + b↑
Ctrl + b↓
Ctrl + b→
Ctrl + b←
// gotcha
Selection is by screen geometry, not pane number, so in an asymmetric layout the pane "above" may not be the one you'd guess. If focus doesn't land where you expect, use Ctrl+b q to see the pane numbers and orient yourself.