mac fixes

com.unity.uiwidgets/Runtime/services/asset_bundle.cs

             var completer = Completer.create();
             var isolate = Isolate.current;
             var panel =UIWidgetsPanelWrapper.current.window;
-            panel.startCoroutine(_loadCoroutine(key, completer, isolate));
+            if (panel.isActive()) {
+                panel.startCoroutine(_loadCoroutine(key, completer, isolate));
+            }
             return completer.future.to<byte[]>();
         }
 

engine/src/shell/platform/unity/darwin/macos/uiwidgets_system.h

 #include <cstdarg>
 #include <set>
 #include <unordered_map>
+#include <mutex>
 
 #include "Unity/IUnityInterface.h"
 #include "Unity/IUnityUIWidgets.h"
 
   TimePoint next_uiwidgets_event_time_ = TimePoint::clock::now();
   std::set<UIWidgetsPanel*> uiwidgets_panels_;
+
+  std::mutex task_mutex_;
 };
 
 }  // namespace uiwidgets

engine/src/shell/platform/unity/darwin/macos/uiwidgets_system.mm

 
 void UIWidgetsSystem::GfxWorkerCallback(int eventId, void* data) {
   const fml::closure task(std::move(gfx_worker_tasks_[eventId]));
-  gfx_worker_tasks_.erase(eventId);
+
+  {
+    std::scoped_lock lock(task_mutex_);
+    gfx_worker_tasks_.erase(eventId);
+  }
-  last_task_id_++;
-
-  gfx_worker_tasks_[last_task_id_] = task;
+  {
+    std::scoped_lock lock(task_mutex_);
+    last_task_id_++;
+    gfx_worker_tasks_[last_task_id_] = task;
+  }
   unity_uiwidgets_->IssuePluginEventAndData(&_GfxWorkerCallback, last_task_id_,
                                             nullptr);
 }