What a pain in the butt tmux is, every release they seem to add/remove things and make every tutorial out there irrelevant. Much of the stuff here doesn’t work anymore on 3.1, as you can see scrolling through the issues above. It’s complicated further by macOS/other terminals swallowing keys on the system level and/or not sending the correct codes. This article needs a serious overhaul with current versions of iTerm/Terminal.app and latest tmux. For instance ‘bind -t’ does not work anymore, etc. the list is endless.
It’s seems that the keybinding for travelling to the last active window has changed this line in my config file does the trick :
bind l last-window