By default minimize real fullscreen windows when they lose focus so the desktop video mode is restored.

This fixes https://github.com/libsdl-org/SDL/issues/4039

src/video/SDL_video.c

@@ -2887,6 +2887,8 @@ SDL_OnWindowFocusGained(SDL_Window * window)
 static SDL_bool
 ShouldMinimizeOnFocusLoss(SDL_Window * window)
 {
+    const char *hint;
+
     if (!(window->flags & SDL_WINDOW_FULLSCREEN) || window->is_destroying) {
         return SDL_FALSE;
     }
@@ -2902,12 +2904,21 @@ ShouldMinimizeOnFocusLoss(SDL_Window * window)
 #ifdef __ANDROID__
     {
         extern SDL_bool Android_JNI_ShouldMinimizeOnFocusLoss(void);
-        if (! Android_JNI_ShouldMinimizeOnFocusLoss()) {
+        if (!Android_JNI_ShouldMinimizeOnFocusLoss()) {
             return SDL_FALSE;
         }
     }
 #endif
 
+    /* Real fullscreen windows should minimize on focus loss so the desktop video mode is restored */
+    hint = SDL_GetHint(SDL_HINT_VIDEO_MINIMIZE_ON_FOCUS_LOSS);
+    if (!hint || !*hint || SDL_strcasecmp(hint, "auto") == 0) {
+        if ((window->flags & SDL_WINDOW_FULLSCREEN_DESKTOP) == SDL_WINDOW_FULLSCREEN_DESKTOP) {
+            return SDL_FALSE;
+        } else {
+            return SDL_TRUE;
+        }
+    }
     return SDL_GetHintBoolean(SDL_HINT_VIDEO_MINIMIZE_ON_FOCUS_LOSS, SDL_FALSE);
 }