GameWindow.SetTitle

Задает заголовок окна.

using UnityEngine;
using UnityEngine.Windowing;

public class SetWindowTitleExample : MonoBehaviour
{
    AsyncOperation asyncOperation = null;

    void Start()
    {
        var window = GameWindow.Main;
        asyncOperation = window.SetTitle("My Game Window");
    }

    void Update()
    {
        if (asyncOperation != null && asyncOperation.isDone)
        {
            Debug.Log("Window title set successfully.");
            asyncOperation = null;
        }
    }
}