The dummy video driver check is now covered by explicitly checking for cocoa above.

src/video/SDL_video.c

@@ -1184,27 +1184,25 @@ SDL_UpdateFullscreenMode(SDL_Window * window, SDL_bool fullscreen)
         if (window->is_destroying && (window->last_fullscreen_flags & FULLSCREEN_MASK) == SDL_WINDOW_FULLSCREEN_DESKTOP)
             return 0;
     
-        if (!_this->is_dummy) {
-            /* If we're switching between a fullscreen Space and "normal" fullscreen, we need to get back to normal first. */
-            if (fullscreen && ((window->last_fullscreen_flags & FULLSCREEN_MASK) == SDL_WINDOW_FULLSCREEN_DESKTOP) && ((window->flags & FULLSCREEN_MASK) == SDL_WINDOW_FULLSCREEN)) {
-                if (!Cocoa_SetWindowFullscreenSpace(window, SDL_FALSE)) {
-                    return -1;
-                }
-            } else if (fullscreen && ((window->last_fullscreen_flags & FULLSCREEN_MASK) == SDL_WINDOW_FULLSCREEN) && ((window->flags & FULLSCREEN_MASK) == SDL_WINDOW_FULLSCREEN_DESKTOP)) {
-                display = SDL_GetDisplayForWindow(window);
-                SDL_SetDisplayModeForDisplay(display, NULL);
-                if (_this->SetWindowFullscreen) {
-                    _this->SetWindowFullscreen(_this, window, display, SDL_FALSE);
-                }
+        /* If we're switching between a fullscreen Space and "normal" fullscreen, we need to get back to normal first. */
+        if (fullscreen && ((window->last_fullscreen_flags & FULLSCREEN_MASK) == SDL_WINDOW_FULLSCREEN_DESKTOP) && ((window->flags & FULLSCREEN_MASK) == SDL_WINDOW_FULLSCREEN)) {
+            if (!Cocoa_SetWindowFullscreenSpace(window, SDL_FALSE)) {
+                return -1;
+            }
+        } else if (fullscreen && ((window->last_fullscreen_flags & FULLSCREEN_MASK) == SDL_WINDOW_FULLSCREEN) && ((window->flags & FULLSCREEN_MASK) == SDL_WINDOW_FULLSCREEN_DESKTOP)) {
+            display = SDL_GetDisplayForWindow(window);
+            SDL_SetDisplayModeForDisplay(display, NULL);
+            if (_this->SetWindowFullscreen) {
+                _this->SetWindowFullscreen(_this, window, display, SDL_FALSE);
             }
+        }
 
-            if (Cocoa_SetWindowFullscreenSpace(window, fullscreen)) {
-                if (Cocoa_IsWindowInFullscreenSpace(window) != fullscreen) {
-                    return -1;
-                }
-                window->last_fullscreen_flags = window->flags;
-                return 0;
+        if (Cocoa_SetWindowFullscreenSpace(window, fullscreen)) {
+            if (Cocoa_IsWindowInFullscreenSpace(window) != fullscreen) {
+                return -1;
             }
+            window->last_fullscreen_flags = window->flags;
+            return 0;
         }
     }
 #elif __WINRT__ && (NTDDI_VERSION < NTDDI_WIN10)