Why is this MeshRenderer null?

The following line fails in my class:

MeshRenderer nRenderer = _Sphere.AddComponent<MeshRenderer>();

This is the entire class. All works except the mentioned line.

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class SphereMaker : MonoBehaviour
{
    private GameObject _Sphere;

    void Start()
    {
        _Sphere = GameObject.CreatePrimitive(PrimitiveType.Sphere);
        _Sphere.AddComponent<MeshFilter>();

        MeshRenderer nRenderer = _Sphere.AddComponent<MeshRenderer>();
        Material nMat = new Material(Shader.Find("Universal Render Pipeline/Lit"));//I'm using the URP

        if (nMat == null)
        {
            Debug.LogError("no mat!!\n");
        }
        nMat.color = Color.red;

        nRenderer.material = nMat;

        float fSize = 0.4f;

        _Sphere.transform.localScale = new Vector3(fSize, fSize, fSize);
        _Sphere.transform.position = new Vector3(0, 0, 0);

    }
}

Does anybody see what I'm doing wrong?

Thank you!