Fixed that the paddles can cross the floor if you run the "Pong" game in the i3 window manager.

2d/pong/project.godot

@@ -22,7 +22,7 @@ window/size/width=640
 window/size/height=400
 window/dpi/allow_hidpi=true
 window/stretch/mode="2d"
-window/stretch/aspect="expand"
+window/stretch/aspect="keep"
 stretch_2d=true
 
 [gdnative]