Helps to modify the iOS home button parameters for each new scene or canvas on awake, you may consider add just one instance per scene.

iOSHomeButton.cs

using UnityEngine;

#if UNITY_IOS
using System.Collections.Generic;
using UnityEngine.UI;
#endif

/// <summary>
/// iOS Home Button.
/// 
/// <para>
/// Helps to modify the iOS home button parameters for each new scene or
/// canvas on awake, you may consider add just one instance per scene.
/// </para>
/// 
/// <para> By Javier García | @jvrgms | 2019 </para>
/// </summary>
[RequireComponent (typeof (Canvas))]
public class IOSHomeButton: MonoBehaviour {



    #region Class Members

    [SerializeField]
    private bool _hideHomeButton;       //  Flag to hide home button.

    [SerializeField]
    private bool _attenuateHomeButton;  //  Flag to attenuate home button.

    [SerializeField]
    private bool _usePadding;           //  Flag to create a padding.

    [SerializeField]
    private Sprite _bezelSprite;        //  Bezel Sprite for padding.


    //  References for Padding, Background and Bazel here created.
    private GameObject Padding { get; set; }
    private GameObject Background { get; set; }
    private GameObject Bezel { get; set; }

    #endregion



    #region Static Accessors

    public static IOSHomeButton Instance { get; private set; }

    /// <summary> Gets or sets a value indicating whether HomeButton
    /// is hide. </summary>
    /// <value><c>true</c> if hide; otherwise, <c>false</c>.</value>
    public static bool Hide {

        #if UNITY_IOS
        get {
            return UnityEngine.iOS.Device.hideHomeButton;
        }
        set {
            UnityEngine.iOS.Device.hideHomeButton = value;
            if (Instance)
                Instance._hideHomeButton = value;
        }

        #else
        get { return true; }
        set {
            Debug.LogWarning (
                string.Concat(
                    "The value ",  value,
                    " just can be used in iOS platform."
                )
            );
        }
        #endif
    }

    /// <summary> Gets or sets a value indicating whether Home Button
    /// is attenuate. </summary>
    /// <value><c>true</c> if attenuate; otherwise, <c>false</c>.</value>
    public static bool Attenuate {

        #if UNITY_IOS
        get {
            return
                UnityEngine.iOS.Device.deferSystemGesturesMode !=
                UnityEngine.iOS.SystemGestureDeferMode.None;
        }
        set {
            UnityEngine.iOS.Device.deferSystemGesturesMode = value ?
            UnityEngine.iOS.SystemGestureDeferMode.BottomEdge :
            UnityEngine.iOS.SystemGestureDeferMode.None;
            if (Instance)
                Instance._attenuateHomeButton = value;
        }

        #else
        get { return true; }
        set {
            Debug.LogWarning (
                string.Concat (
                    "The value ", value,
                    " just can be used in iOS platform."
                )
            );
        }
        #endif
    }

    #endregion



    #region Private Accessors
    //  These private accessors are used to avoid read only warning on
    //  visual studio, also you can add #pragma warning disable IDE0044
    //  and  #pragma warning restore RECS0029 before and after the 
    //  declaration of the variable.

    //  Flag to know if the home button must be hide.
    private bool HideHomeButton {
        get { return _hideHomeButton; }
        set { _hideHomeButton = value; }
    }

    //  Flag to know if the home button must be attenueated.
    private bool AttenuateHomeButton {
        get { return _attenuateHomeButton; }
        set { _attenuateHomeButton = value; }
    }

    //  Flag to create a padding.
    private bool UsePadding {
        get { return _usePadding; }
        set { _usePadding = value; }
    }

    //  Bezel Sprite for padding.
    private Sprite BezelSprite {
        get { return _bezelSprite; }
        set { _bezelSprite = value; }
    }

    #endregion



    #region MonoBehaviour Overrides

    //  Called on awake.
    private void Awake () {

        Instance = this;

        #if UNITY_IOS

        Hide = HideHomeButton;
        Attenuate = AttenuateHomeButton;

        if (UsePadding) {

            //  Padding Creation. Container for current canvas content.
            Padding = new GameObject (
                name: "Padding",
                components: typeof (RectTransform)
            );
            Padding.transform.SetParent (transform, false);

            RectTransform paddingTransform = Padding.GetComponent<RectTransform> ();
            paddingTransform.anchorMin = Vector2.zero;
            paddingTransform.anchorMax = Vector2.one;
            paddingTransform.offsetMax = Vector2.zero;
            paddingTransform.offsetMin = Vector2.up * 40f;

            List<Transform> childs = new List<Transform> ();
            for (int i = 0; i < transform.childCount; i++)
                childs.Add (transform.GetChild (i));
            childs.ForEach (t => t.SetParent (Padding.transform, false));


            //  Padding Background. Avoid to show camera background.
            Background = new GameObject (
                name: "Padding Background",
                components: typeof (RectTransform)
            );
            Background.transform.SetParent (transform, false);

            RectTransform backgroundTransform = Background.GetComponent<RectTransform> ();
            backgroundTransform.offsetMin = Vector2.zero;
            backgroundTransform.offsetMax = Vector2.zero;
            backgroundTransform.anchorMin = Vector2.zero;
            backgroundTransform.anchorMax = Vector2.right;
            backgroundTransform.sizeDelta = Vector2.up * 40f;
            backgroundTransform.pivot = new Vector2 (0.5f, 0f);

            Image backgroundImage = Background.AddComponent<Image> ();
            backgroundImage.color = Color.black;

            //  Bezel to simulate the bezel iPad.
            Bezel = new GameObject (
                name: "Bezel",
                components: typeof (RectTransform)
            );
            Bezel.transform.SetParent (transform, false);

            RectTransform bezelTransform = Bezel.GetComponent<RectTransform> ();
            bezelTransform.anchorMin = Vector2.zero;
            bezelTransform.anchorMax = Vector2.one;
            bezelTransform.offsetMax = Vector2.zero;
            bezelTransform.offsetMin = Vector2.up * 40f;

            Image bezelImage = Bezel.AddComponent<Image> ();
            bezelImage.sprite = BezelSprite;
            bezelImage.color = Color.black;
            bezelImage.type = Image.Type.Sliced;
            bezelImage.raycastTarget = false;

        }

        #endif
    }

    //  Called on destroy. Claen the Instance reference.
    private void OnDestroy () {
        if (Instance == this)
            Instance = null;
    }

#endregion
}