Physics Material

using UnityEngine;

public class SurfaceMaterialSwapper : MonoBehaviour
{
  public PhysicMaterial normalMat, iceMat, rubberMat;
  Collider col;

  void Start() => col = GetComponent<Collider>();

  void OnCollisionStay(Collision collision)
  {
      // Read the ground tag
      string tag = collision.gameObject.tag;

      col.material = tag switch
      {
          "Ice"    => iceMat,
          "Rubber" => rubberMat,
          _        => normalMat,
      };
  }

  void OnCollisionExit(Collision _)
  {
      col.material = normalMat; // Restore when leaving the ground
  }
}

using UnityEngine;

// Create and own a PhysicMaterial at runtime — no Project asset
public class DynamicPhysicsMaterial : MonoBehaviour
{
  Collider col;
  PhysicMaterial dynMat;

  [Range(0f, 1f)] public float friction = 0.4f;
  [Range(0f, 1f)] public float bounciness = 0f;

  void Awake()
  {
      col = GetComponent<Collider>();

      // Runtime PhysicMaterial, no Project asset needed
      dynMat = new PhysicMaterial("Dynamic")
      {
          dynamicFriction  = friction,
          staticFriction   = friction * 1.2f,
          bounciness       = bounciness,
          frictionCombine  = PhysicMaterialCombine.Average,
          bounceCombine    = PhysicMaterialCombine.Maximum
      };

      col.material = dynMat;
  }

  // Call from elsewhere to change live (e.g. character frozen)
  public void SetIce()
  {
      dynMat.dynamicFriction = 0.01f;
      dynMat.staticFriction  = 0.01f;
      col.material = dynMat; // Re-assign so Unity picks up the new values
  }
}