SaveRenderTextureToJPG.cs

using UnityEngine;
using System.Collections;
using System.IO;

public class SaveRenderTextureToJPG : MonoBehaviour
{
    [SerializeField]
    Renderer targetRenderer;

    private void Start()
    {
        if (targetRenderer == null)
            targetRenderer = GetComponent<MeshRenderer>();
    }

    WaitForEndOfFrame frameEnd = new WaitForEndOfFrame();

    IEnumerator savePng()
    {
        yield return frameEnd;

        var RenderTextureRef = targetRenderer.material.GetTexture("_MainTex") as Texture2D;
        Debug.Log($"{RenderTextureRef.width} / {RenderTextureRef.height}");

        byte[] bytes = RenderTextureRef.EncodeToJPG();
        Object.Destroy(RenderTextureRef);

        //Write to a file in the project folder
        File.WriteAllBytes(Application.dataPath + "/../SavedScreen.jpg", bytes);
    }


    private void OnGUI()
    {
        if (GUI.Button(new Rect(10, 10, 200, 40), "SAVE"))
        {
            StartCoroutine("savePng");
        }
    }
}

SaveRenderTextureToPng.cs

using UnityEngine;
using System.Collections;
using System.IO;

public class SaveRenderTextureToPng : MonoBehaviour
{
    [SerializeField]
    Renderer targetRenderer;

    private void Start()
    {
        if (targetRenderer == null)
            targetRenderer = GetComponent<MeshRenderer>();
    }

    bool isCapture = false;

    WaitForEndOfFrame frameEnd = new WaitForEndOfFrame();

    IEnumerator savePng()
    {
        yield return frameEnd;

        var RenderTextureRef = targetRenderer.material.GetTexture("_MainTex") as Texture2D;
        Debug.Log($"{RenderTextureRef.width} / {RenderTextureRef.height}");

        byte[] bytes = RenderTextureRef.EncodeToPNG();
        Object.Destroy(RenderTextureRef);

        //Write to a file in the project folder
        File.WriteAllBytes(Application.dataPath + "/../SavedScreen.png", bytes);
    }


    private void OnGUI()
    {
        if (GUI.Button(new Rect(10, 10, 200, 40), "SAVE"))
        {
            StartCoroutine("savePng");
        }
    }
}