Quad is turing black when changing it's texture in unity

I am building an Android application, which will read images from ‘/sdcard/Documents/’ and then display them on a Quad, using unity3D. When I test the app inside Unity in play mode (using images from an external path), the texture of the quad is updated according to the image, but when I build the APK and test it on the device, the quad turns black.

Here’s the code I am using:

public class ShowImage : MonoBehaviour {
    [SerializeField] GameObject quad;
    int count = 0;
    Material quadMaterial;
    string extPath;

    void Start() {
        AndroidJavaClass envClass = new AndroidJavaClass("android.os.Environment");
        AndroidJavaObject extStorageDir = envClass.CallStatic<AndroidJavaObject>("getExternalStorageDirectory");
        extpath = extStorageDir.Call<string>("getAbsolutepath");
        quadMaterial = quad.GetComponent<Renderer>().material;
    void Update() {
        if (File.Exist($"{extPath}/Documents/temp_{count}.png")) {
            byte[] imageData = File.ReadAllBytes($"{extPath}/Documents/temp_{count}.png");
            Texture2D texture = new Texture2D(2, 2);
            // Texture2D texture = new Texture2D(2, 2, TextureFormat.ARG32, true);
            // ImageConversion.LoadImage(texture, imageData, true);
            quadMaterial.mainTexture = texture;

I put some debug statements also, the image is being read, as imageData.Length is returning the correct value. Also, I am not getting any errors, I checked the logs using ADB.