A simple script that lets you call UnityEvents based on the current platform (Windows, Mac, Debug, Steam, etc)

PlatformBrancher.cs

using UnityEngine;
using UnityEngine.Events;

public class PlatformBrancher : MonoBehaviour
{
    public PlatformEvent[] onEnable;
    public PlatformEvent[] onStart;
    public PlatformEvent[] onDisable;
    [Tooltip("to be called manually via PlatformBrancher.OnInvoke()")]
    public PlatformEvent[] onInvoke;

    private void Start()
    {
        for (int i = 0; i < onStart.Length; i++)
        {
            FireEvent(onStart[i]);
        }
    }

    private void OnEnable()
    {
        for (int i = 0; i < onEnable.Length; i++)
        {
            FireEvent(onEnable[i]);
        }
    }

    private void OnDisable()
    {
        for (int i = 0; i < onDisable.Length; i++)
        {
            FireEvent(onDisable[i]);
        }
    }

    public void OnInvoke()
    {
        for (int i = 0; i < onInvoke.Length; i++)
        {
            FireEvent(onInvoke[i]);
        }
    }

    void FireEvent(PlatformEvent platformEvent)
    {
        if (platformEvent.platform == Platform.All)
        {
            platformEvent.unityEvent.Invoke();
        }
#if UNITY_STANDALONE_WIN || UNITY_EDITOR_WIN
        if (platformEvent.platform == Platform.Windows)
        {
            platformEvent.unityEvent.Invoke();
        }
#endif
#if UNITY_STANDALONE_OSX || UNITY_EDITOR_OSX
        if (platformEvent.platform == Platform.Mac)
        {
            platformEvent.unityEvent.Invoke();
        }
#endif
#if STEAM
        if (platformEvent.platform == Platform.Steam)
        {
            platformEvent.unityEvent.Invoke();
        }
#endif
#if DEMO
        if (platformEvent.platform == Platform.Demo)
        {
            platformEvent.unityEvent.Invoke();
        }
#endif
        if (Debug.isDebugBuild)
        {
            if (platformEvent.platform == Platform.Debug)
            {
                platformEvent.unityEvent.Invoke();
            }
        }
    }
}

[System.Serializable]
public struct PlatformEvent
{
    public Platform platform;
    public UnityEvent unityEvent;
}

public enum Platform
{
    All,
    Windows,
    Mac,
    Steam,
    Demo,
    Debug
}