Question Game freeze when InstantiatingAsync

Hello,

The frame freezes when I run this code.
I tried using async/await, but that throws an error saying it must be run on the Main thread.
As I understand it, changes to a UI element must be done on the Main thread and starting the method with await will start the operation on a different thread.

What are the options to run this without blocking the Main thread?

Code (CSharp):

1. private void InstantiateStuff(){
2.  
3.      // contentList has 1000 items
4.  
5.      foreach (var item in contentList)
6.      {
7.              prefab.InstantiateAsync(Vector3.zero, Quaternion.identity).Completed +=
8.                 (AsyncOperationHandle<GameObject> op) =>
9.                 {
10.                     GameObject uiElement= op.Result;
11.                     // Plenty more logic here populating the new uiElement from item
12.                 };
13.      }