Unity - Auto-hide UI in GameView when not in play mode.

GameWindowHideUIUntilPlay.cs

using UnityEngine;

//Place on Camera you want to stop rendering UI while out of Play mode.
//UI Canvas needs to have its "Render Mode" be ing either "World Space" or "Screen Space - Camera" for this to work.
[ExecuteAlways, ExecuteInEditMode, RequireComponent(typeof(Camera))]
public class GameWindowHideUIUntilPlay : MonoBehaviour
{
    void OnEnable()
    {
        ToggleUIDisplay(Application.isPlaying);
    }
    
    void OnDisable()
    {
        ToggleUIDisplay(true);
    }

    void ToggleUIDisplay(bool visible)
    {
        var cam = GetComponent<Camera>();

        if(visible)
        {
            cam.cullingMask |=  LayerMask.GetMask("UI"); //Add UI Layer from camera
        }
        else
        {
            cam.cullingMask &= ~LayerMask.GetMask("UI"); //Remove UI Layer from camera
        }
    }
}