Hi there,
I've played this game made with Godot 2 and it is responsive.
https://cowthing.itch.io/mushroom-towers
So it must be possible to catch the event of resize_screen
(pick to right one ^^) and replace the elements in there, or use containers ?
In the game above there is event the particles moving on the screen, in fact all the graphics fill the window. Play with it in windowed mode and resize it!