Hard to believe, but I think fullscreen truly works, even through sleep.

desktop/src-common/advent/screens/credits.clj

@@ -11,6 +11,7 @@
   (:import [com.badlogic.gdx.graphics Pixmap Pixmap$Filter Texture Texture$TextureFilter]
            [com.badlogic.gdx.graphics.g2d TextureRegion]
            [com.badlogic.gdx.scenes.scene2d.utils Align]
+           [com.badlogic.gdx.utils.viewport FitViewport]
            [com.badlogic.gdx Application Audio Files Game Gdx Graphics Input
             InputMultiplexer InputProcessor Net Preferences Screen]))
 
@@ -32,7 +33,8 @@
     )
   
   :on-render
-  (fn [screen [entities]]
+  (fn [{:keys [^FitViewport viewport] :as screen} [entities]]
+    (.apply viewport)
     (let [entities (utils/apply-tweens screen entities (:tweens entities))]
       
       (render! screen [(:the-end entities) (:fade entities)])