Jump like teleporting - unity3d

Question

I'm working on unity and am trying to give my player character a jump button however when he jump he teleport up not jumping
private float speed = 10f;
private bool canjump = false;
private Rigidbody rb;
private float jump =100f;
private float movementX;
private float movementy;
public bool isJumping;
private float jumpdecay =20f;
public float fallmultipler = 2.5f;
public float lowjumpmultiplier = 2f;
void Start()
{
rb = GetComponent<Rigidbody>();
}
private void OnMove(InputValue movementValue)
{
Vector2 movementVector = movementValue.Get();
movementX = movementVector.x;
}
private void Update()
{
Vector3 movement = new Vector2(movementX, 0);
rb.velocity = movement * speed;
if (Input.GetKeyDown(KeyCode.Space))
{
canjump = true;
}
}
void OnTriggerEnter(Collider collision)
{
if(collision.gameObject.tag == "ground")
{
isJumping = false;
}
}
void OnTriggerExit(Collider collision)
{
isJumping = true;
}
private void FixedUpdate()
{
if (canjump & isJumping == false)
{
rb.velocity = Vector3.up * jump;
canjump = false;
}
}

Answer 1

It's happen because on Update you change your velocity including the y and then every frame your y axis of the velocity vector become 0.
to fix that you should save your y and replace after modify your velocity.
change inside your code in the update method this:
Vector3 movement = new Vector2(movementX, 0);
rb.velocity = movement * speed;
with this:
Vector3 movement = new Vector2(movementX, 0);
float currentVelocity = rb.velocity.y;
rb.velocity = movement * speed;
rb.velocity = new Vector3(rb.velocity.x, currentVelocity, rb.velocity.z);
if it's help you, please mark this answer as the good answer, if not please let me know and I will help you.

Answer 2

You are reseting the y velocity inside of update
Vector3 movement = new Vector2(movementX, 0);
rb.velocity = movement * speed;
Try someting like
rb.velocity = new Vector2(movementX * speed, rb.velocity.y)
rb.velocity.y returns current y velocity, because of that said velocity remains unchanged, allowing for the jump to work normally