Can't implement jumping to 2D side-scroller click-to-move.

So I'm trying to make a 2d side-scroller platformer, but instead of using traditional "Left/Right" arrow keys or "A/D", I've created a click to move controller that only moves the player horizontally. However I'm trying to implement a jump mechanic but I cannot seem to get the jump to work right with the click to move controls. Whenever I jump the character seems to have a varied jump velocity every time. Also when I walk off of platforms (to get to another platform below) the character seems to stop midair for a second then actually start to fall and I also think it is because of how my click to move controller is set up. Any suggestions/tips would be greatly appreciated! Here is my movement code:

 public Rigidbody2D rb;

 public float speed = 10f;
 private Vector2 targetPosition;
 private bool isMoving = false;

 //grounded check for jumps
 public float jumpVelocity = 10f;
 private bool isGrounded;
 public Transform groundCheck;
 public float checkRadius;
 public LayerMask whatIsGround;

 private void Update()
 {
     if (Input.GetMouseButton(0))
     {
         SetTargetPosition();
     }

     if (Input.GetKey(KeyCode.LeftShift))
     {
         isMoving = false;
     }

     if (Input.GetKeyDown(KeyCode.Space) && isGrounded == true)
     {
         rb.velocity = Vector2.up * jumpVelocity * Time.deltaTime;
     }

     if (transform.position.y == targetPosition.y && transform.position.x == targetPosition.x)
     {
         isMoving = false;
     }
 }
 private void FixedUpdate()
 {
     isGrounded = Physics2D.OverlapCircle(groundCheck.position, checkRadius, whatIsGround);

     if (isMoving)
     {
         rb.position = Vector3.MoveTowards(rb.position, targetPosition, speed * Time.deltaTime);
     }
 }

 private void SetTargetPosition()
 {
     targetPosition = Camera.main.ScreenToWorldPoint(Input.mousePosition);
     targetPosition.y = transform.position.y;

     isMoving = true;
 }