Completely Get Rid of Borders

xprop
my old post

or according to arch-wiki

To get only the app_id’s of all open windows use:
swaymsg -t get_tree | grep "app_id"

But it may not be as simple

If the app_id happens to be null for some windows, you might have to use the class and/or the instance attributes to enable floating mode/window assignments. You can search the output and create fine grained rules for your windows.

~/.config/sway/config

for_window [app_id=“galculator”] floating enable
assign [class=“firefox”] → 3
assign [class=“^Urxvt$” instance=“^htop$”] → 9