object in Jump&Run-Game is flickering when hitting boundaries - how to avoid?

I’m trying to create a 3D-Jump&Run-Game but I have this issue with the flickering.
My assumption was that since the player’s pivot is clamped to the borders, half of the player leaves the boundaries (reason for flickering).

So I did this (but unfortunately it is not working) :

public class PlayerController : MonoBehaviour
{

Rigidbody myRigidbody;
public float speed = 6f;


/* variables to limit movement range in x-axis
 * border values determined by visual estimate in scene view
 * issue: the player's pivot is clamped to the borders --> half of the player leaves the border --> 
    flickering
 * modify border values and add/substract half of the player's size (done in RunHandler())
 */

float objectWidth;
float minX = -1.601f;
float maxX = 1.671f;

void Start()
{
    //compute player's size and devide it by 2 --> for keeping gameobject within boundaries
    objectWidth = transform.GetComponent<MeshRenderer>().bounds.size.x / 2;

    myRigidbody = GetComponent<Rigidbody>();
}

void FixedUpdate()
{
    RunHandler();
}

void RunHandler()
{
    float moveVertical = Input.GetAxis("Vertical");
    float moveHorizontal = Input.GetAxis("Horizontal");

    Vector3 movement = new Vector3(moveHorizontal, 0f, moveVertical);
    myRigidbody.MovePosition(transform.position + (movement * speed));
    
    /*
     * set a variable to the position
     * modify the variable to keep x within minX and maxX
     * set the transform position to the modified vector
    */
    Vector3 currentPosition = transform.position;
    currentPosition.x = Mathf.Clamp(currentPosition.x, minX + objectWidth, maxX - objectWidth);
    transform.position = currentPosition;
    
}

}

Why not just use Colliders as boundaries

When you are dealing with physics using a rigidbody, never use transform.position unless you set your rigidbody to kinematic and zero out its velocity.

To fix your problem you need to change all your transform.position to myRigidbody.position.