gpu rendering is the defaults on gtk and avalonia native

both these platforms will fallback to SW render if GPU not available.

src/Avalonia.Native/AvaloniaNativePlatform.cs

@@ -120,7 +120,7 @@ namespace Avalonia.Native
     {
         public AvaloniaNativeMacOptions MacOptions { get; set; }
         public bool UseDeferredRendering { get; set; } = true;
-        public bool UseGpu { get; set; } = false;
+        public bool UseGpu { get; set; } = true;
         internal AvaloniaNativeOptions(IAvaloniaNativeFactory factory)
         {
             var mac = factory.GetMacOptions();

src/Gtk/Avalonia.Gtk3/Gtk3Platform.cs

@@ -148,8 +148,8 @@ namespace Avalonia.Gtk3
 
     public class Gtk3PlatformOptions
     {
-        public bool? UseDeferredRendering { get; set; }
+        public bool? UseDeferredRendering { get; set; } = true;
-        public bool? UseGpuAcceleration { get; set; }
+        public bool? UseGpuAcceleration { get; set; } = true;
         public ICustomGtk3NativeLibraryResolver CustomResolver { get; set; }
     }
 }