WebGL Disappearing RawImage

Test.cs

using System;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;
using Random = UnityEngine.Random;

public class Test : MonoBehaviour
{
    public RawImage rawImage;
    public int XRESOLUTION = 15, YRESOLUTION = 10;
    public int pixelsPerCell;

    private RenderTexture rt;
    private Texture2D tex;

    private void Start()
    {
        int _xRes = XRESOLUTION * pixelsPerCell;
        int _yRes = YRESOLUTION * pixelsPerCell;
        rt = new RenderTexture(_xRes, _yRes, 0);
        tex = new Texture2D(_xRes, _yRes, TextureFormat.ARGB32, false);
        
        rt.filterMode = FilterMode.Point;
        rt.wrapMode = TextureWrapMode.Clamp;
        rt.format = RenderTextureFormat.ARGB32;
        rt.useMipMap = false;

        rawImage.texture = rt;
    }

    private void FixedUpdate()
    {
        int _xRes = XRESOLUTION * pixelsPerCell;
        int _yRes = YRESOLUTION * pixelsPerCell;
        
        RenderTexture.active = rt;
        var pixels =  tex.GetPixels(0, 0, _xRes, _yRes);
        
        int pIndex = 0;
            
        // i think the weird display comes in here. We need to be doing pixels per cell implementation
        for (int y = 0; y < YRESOLUTION; y++)
        {
            for (int x = 0; x < XRESOLUTION; x++)
            {
                pixels[pIndex++] = Random.ColorHSV();
            }   
        }
        tex.SetPixels(pixels);
        tex.Apply();
        Graphics.CopyTexture(tex, 0, 0, 0, 0, _xRes, _yRes, rt, 0, 0, 0, 0);
        RenderTexture.active = null;
    }
}