Texture2D.ReadPixels and not lose image quality

How do I use Texture2D and not lose image quality?

When the game starts, there are a random number of splats enabled.

Then when the user presses SPACE, the game captures the screen using Texture2D.ReadPixels and pushes that texture to a background texture. After which a random number of splats are enabled.

However, the captured image loses its quality. So instead of continuously adding splats on top of splats, old splats will eventually fade away entirely.

I am using the following code:

 _mainTexture = new Texture2D(Screen.width, Screen.height, TextureFormat.RGB24, false);

 yield return new WaitForEndOfFrame();
 _mainTexture.ReadPixels(new Rect(0, 0, Screen.width, Screen.height), 0, 0, false);
 _mainTexture.Apply();
 
 renderer.material.mainTexture = _mainTexture;