SampleSystem3.cs

using Unity.Entities;

public class SampleSystem3 : ComponentSystem
{
    protected override void OnUpdate()
    {
        Entities.ForEach((Entity entity, ref Score score) => {

            // EntityManager.DestroyEntity(entity) // エラーが出る
            PostUpdateCommands.DestroyEntity(entity); // こちらならOK
        });
    }
}