Merge pull request #12163 from owen-young/default-fullscreen

osu.Game/OsuGame.cs

@@ -531,6 +531,13 @@ namespace osu.Game
             SentryLogger.Dispose();
         }
 
+        protected override IDictionary<FrameworkSetting, object> GetFrameworkConfigDefaults()
+            => new Dictionary<FrameworkSetting, object>
+            {
+                // General expectation that osu! starts in fullscreen by default (also gives the most predictable performance)
+                { FrameworkSetting.WindowMode, WindowMode.Fullscreen }
+            };
+
         protected override void LoadComplete()
         {
             base.LoadComplete();