So vim and neovim (and probably other programs too) check terminfo for the XT Boolean flag and if it is found they enable the focus tracking features.
Outside tmux my terminal has the XT capability (tput XT runs successfully). Inside tmux the same command returns the error:
tput: unknown terminfo capability 'XT'

However clearly tmux has focus tracking capability, since I explicitly enabled it with set -g focus-events on, so I would expect it to set the XT capability.
I tried using terminal overrides: set -as terminal-overrides ",*:Tc:XT"
But this doesn't work, probably because this only overrides the outside terminal terminfo.

Is there any workaround how I can use tmux-256color and have the XT capability set? My current workaround is to use set -g default-terminal "xterm-256color", which does set the XT capability.

• tmux version: next-3.3
• $TERM inside and outside of tmux: Outside: xterm-256color, Inside: tmux-256color

P.S.: screen-256color does not set XT as well.