How can I slide with a character controller

This is what I have so far.

public float SlopeForce;
public float slopeForceRayLength;

public CharacterController controller;

public Transform groundCheck;
public float groundDistance = 0.3f;
public LayerMask groundMask;
public bool Jumping;

Vector3 velocity;
bool isGrounded;

void Start()
{
    
}

// Update is called once per frame
void Update()
{
    Jump();
    physics();
    Movement();
    Crouch();
}

public void Jump()
{
    if (Input.GetButtonDown("Jump") && isGrounded)
    {
        Jumping = true;
        controller.slopeLimit = 90f;
        velocity.y = Mathf.Sqrt(JumpHeight * -2f * gravity);
        controller.slopeLimit = 45f;
        Jumping = false;
    }
}

public void physics()
{
    isGrounded = Physics.CheckSphere(groundCheck.position, groundDistance, groundMask);

    if (isGrounded && velocity.y < 0)
    {
        velocity.y = -2f;
    }

    velocity.y += gravity * Time.deltaTime;

    controller.Move(velocity * Time.deltaTime);
}

public void Movement()
{

    float x = Input.GetAxis("Horizontal");
    float z = Input.GetAxis("Vertical");

    Vector3 move = transform.right * x + transform.forward * z;
    controller.Move(move * speed * Time.deltaTime);

    if((x != 0 || z != 0) && OnSlope())
    {
        controller.Move(Vector3.down * controller.height / 2 * SlopeForce * Time.deltaTime);
    }
}

public void Crouch()
{
    if (Input.GetKeyUp("c"))
    {
        transform.localScale = new Vector3(x:1, y:1, z:1);
    }

    if (Input.GetKeyDown("c"))
    {
        transform.localScale = new Vector3(x:1, y:CrouchHeight, z:1);
    }
}

public bool OnSlope()
{
    if (Jumping)
        return false;

    RaycastHit hit;

    if (Physics.Raycast(transform.position, Vector3.down, out hit, controller.height/2 * slopeForceRayLength))
        if (hit.normal != Vector3.up)
            return true;

    return false;
}

}

@Matt1928 Have you tried adding a physic material to the collider?