How to switch to the previous pane by any shortcut in tmux?
In tmux manual ($man tmux) you can find this section:
select-pane [-DdeLlRU] [-t target-pane] (alias: selectp) Make pane target-pane the active pane in window target-window. If one of -D, -L, -R, or -U is used, respectively the pane below, to the left, to the right, or above the target pane is used. -l is the same as using the last-pane command. -e enables or -d disables input to the pane.So, I think what you want is to use the '-l' flag, which is for switch to last pane. I don't know if there is a default key mapping defined to this task, but you can accomplish this by doing your own bindings. Something like this:
bind -r <your key> select-pane -l