This issue is also happening on 2018.4.36f1

... or set Screen.orientation property in Start() method not in Awake().

Hello.
I have exactly the same issue - I cannot run iOS app. I'm using Unity 2020.3.20. I do have one custom script in which in Awake() I'm setting Screen.orientation = ScreenOrientation.Portrait.
When I disable this line it works ok.

Workaround: use coroutine to change orientation property. In my case in Awake() I'm starting coroutine and waiting 0.1f before setting orientation property.

private IEnumerator ChangeOrientation(ScreenOrientation screenOrientation)
{
yield return new WaitForSeconds(0.1f);
Screen.orientation = screenOrientation;
}