Add this component to the same gameobject as paintcraft CanvasController

SecondCameraCtrl.cs

using PaintCraft.Canvas.Configs;
using PaintCraft.Controllers;
using UnityEngine;
using UnityEngine.Assertions;



[RequireComponent(typeof(CanvasController))]
public class SecondCameraCtrl : MonoBehaviour
{
	[SerializeField] private Color _clearColor = Color.black;
	private CanvasController _canvas;
	private Camera _seconCamera;

	void Awake()
	{		
		if (Display.displays.Length < 2)
		{
			DestroyImmediate(this);
			return;			
		}
		
		if (!Display.displays[1].active)
		{			
			Display.displays[1].Activate();			
		}
	}
	
	void Start(){				
		_canvas = GetComponent<CanvasController>();
		Assert.IsNotNull(_canvas);
		
		InitCameraParams();
		_canvas.OnPageChange += OnPageChange;
		if (_canvas.PageConfig != null)
		{
			OnPageChange(_canvas.PageConfig);
		}		
	}
	
	

	private void InitCameraParams()
	{		
		_seconCamera = GetComponent<Camera>();
		if (_seconCamera == null)
		{			
			_seconCamera = gameObject.AddComponent<Camera>();			
		}
		_seconCamera.targetDisplay = 1;
		_seconCamera.targetTexture = null;
		_seconCamera.orthographic = true;
		_seconCamera.clearFlags = CameraClearFlags.Color;
		_seconCamera.backgroundColor = _clearColor;
		_seconCamera.cullingMask = int.MaxValue;// _canvas.BrushLayerId| _canvas.TempRenderLayerId | 8; //8 is a canvas		
	}

	private void OnDestroy()
	{
		if (_canvas != null)
		{			
			_canvas.OnPageChange -= OnPageChange;
		}
	}

	private void OnPageChange(PageConfig pageConfig)
	{		
		_seconCamera.orthographicSize = pageConfig.GetSize().y / 2.0f;		
	}
}