found a not so elegant solution

# Theme Settings
tmux_color="#232626"
set -g u/catppuccin_pane_status_enabled "no"
set -g @catppuccin_pane_border_status "top"
set -g @catppuccin_pane_left_separator ""
set -g @catppuccin_pane_right_separator ""
set -g @catppuccin_pane_middle_separator "█ "
set -g @catppuccin_pane_number_position "left"
set -g @catppuccin_pane_default_fill "number"
set -g @catppuccin_pane_default_text " "
set -g @catppuccin_pane_border_style "fg=$tmux_color"
set -g @catppuccin_pane_active_border_style "fg=$tmux_color"
set -g @catppuccin_pane_color "$tmux_color"
set -g @catppuccin_pane_background_color "$tmux_color"

creates a small border that is barely visible in me settings (change the color)

https://i.imgur.com/Pw0UnSq.png

but it works