Hi, as I understand you can't join windows the same way as status modules, because of text direction and background nesting

However, I updated code to look closer to your needs. Same approach used in dracula tmux

Config from screenshot:

set -g @catppuccin_window_left_separator " "
set -g @catppuccin_window_right_separator "█"
set -g @catppuccin_window_middle_separator "▕ "
set -g @catppuccin_window_default_fill "none"
set -g @catppuccin_window_current_fill "all"
set -g @catppuccin_window_number_position "right"
set -g @catppuccin_window_connect_separator "yes"

Just created PR, for now problem that I see is with most right separator. To fix this dracula tmux uses fixed icon that renders before all windows.
In this example from dracula icon shows current session (on screenshot only one window, can be confusing)

If we are interested in the same logic, I can create try to implement it

That looks awesome @MykhailoSukhostavets thanks for your work! 🙏 Perfectly what I was trying to express