Photogrammetry in Unity
To edit and create a photogrammetry mesh, read here.
To let other objects interact with the mesh, give it a mesh collider component. In the video example below, the rock wall photogrammetry mesh has around 40 000 tris. It has a mesh collider. The falling spheres are Unity's default Sphere Objects, with a Sphere Collider and a Rigidbody Component that uses Gravity. It has a Physic Material with a slight bounciness. The rock also have a Physics Material to better control the friction and bounciness.
The Stickman is an image animation composed of transparent images. They are tied to a game object that has a Character Controller component. This gameobject's transform is moved forward by script but the Character Controller is in control of the surface movement since it is using gravity.