Implement fix (#8950)

fixes #8261

Xamarin.Forms.Platform.MacOS/NativeToolbarTracker.cs

@@ -140,10 +140,12 @@ namespace Xamarin.Forms.Platform.MacOS
 				AllowsUserCustomization = false,
 				ShowsBaselineSeparator = true,
 				SizeMode = NSToolbarSizeMode.Regular,
-				Delegate = this,
-				CenteredItemIdentifier = TitleGroupIdentifier
+				Delegate = this
 			};
 
+			if (Forms.IsMojaveOrNewer)
+				toolbar.CenteredItemIdentifier = TitleGroupIdentifier;
+
 			return toolbar;
 		}
 

Xamarin.Forms.Platform.iOS/Forms.cs

@@ -38,9 +38,7 @@ namespace Xamarin.Forms
 		static bool? s_isiOS11OrNewer;
 		static bool? s_isiOS13OrNewer;
 		static bool? s_respondsTosetNeedsUpdateOfHomeIndicatorAutoHidden;
-#endif
 
-#if __MOBILE__
 		internal static bool IsiOS9OrNewer
 		{
 			get
@@ -91,6 +89,19 @@ namespace Xamarin.Forms
 				return s_respondsTosetNeedsUpdateOfHomeIndicatorAutoHidden.Value;
 			}
 		}
+#else
+		static bool? s_isMojaveOrNewer;
+
+		internal static bool IsMojaveOrNewer
+		{
+			get
+			{
+				if (!s_isMojaveOrNewer.HasValue)
+					s_isMojaveOrNewer = NSProcessInfo.ProcessInfo.IsOperatingSystemAtLeastVersion(new NSOperatingSystemVersion(10, 14, 0));
+				return s_isMojaveOrNewer.Value;
+			}
+		}
+
 #endif
 
 		static IReadOnlyList<string> s_flags;