TerrainCreateTest.cs

using System.Collections;
using UnityEngine;

public class TerrainCreateTest : MonoBehaviour
{
    private void Start()
    {
        // This should in theory generate a new terrain object.
        TerrainData terrainData = new();
        terrainData.size = new(512, 512, 512);
        Terrain.CreateTerrainGameObject(terrainData);
    }
}