Attach an object to a platform when they collide and move with it.

SnapToPlatform.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class SnapToPlatform : MonoBehaviour
{
    private Vector3 _lastPlatformPosition;
    private Quaternion _lastPlatformRotation;

    public bool IsOnPlatform;
    public GameObject CurrentPlatform;
    public string PlatformLayerName = "Platform";

    void Awake()
    {
        IsOnPlatform = false;
    }

    void OnCollisionEnter(Collision collision)
    {
        foreach (ContactPoint contact in collision.contacts)
        {
            if (contact.otherCollider.gameObject.layer == LayerMask.NameToLayer(PlatformLayerName))
            {
                IsOnPlatform = true;
                CurrentPlatform = contact.otherCollider.gameObject;
            }
        }
    }

    void OnCollisionExit(Collision collision)
    {
        if (collision.gameObject == CurrentPlatform)
        {
            IsOnPlatform = false;
            CurrentPlatform = null;
        }      
    }    

    void Update()
    {
        if (IsOnPlatform)
        {
            var currentPlatformPosition = CurrentPlatform.transform.position;
            var currentPlatformRotation = CurrentPlatform.transform.rotation;

            if (currentPlatformRotation != _lastPlatformRotation)
            {
                var rotationChange = Quaternion.Inverse(_lastPlatformRotation) * currentPlatformRotation;
                transform.rotation = transform.rotation * rotationChange;

            }
            if (currentPlatformPosition != _lastPlatformPosition)
            {
                var positionChange = currentPlatformPosition - _lastPlatformPosition;
                transform.position += positionChange;
            }

            _lastPlatformPosition = CurrentPlatform.transform.position;
            _lastPlatformRotation = CurrentPlatform.transform.rotation;
        }
        
    }

}