Player.cs

using UnityEngine;

public class Player : MonoBehaviour
{
    private CharacterController _controller;
    private PlayerControls _playerInputs;

    [SerializeField]
    private float _moveSpeed = 5f;
    [SerializeField]
    private float _gravity = 10f;
    [SerializeField]
    private float _jumpHeight = 50f;

    private bool _isJumping;

    [SerializeField]
    private float _yVelocity;

    // Start is called before the first frame update
    void Start()
    {
        _controller = GetComponent<CharacterController>();
        _playerInputs = new PlayerControls();
        _playerInputs.Platforming.Enable();
        _playerInputs.Platforming.Jump.performed += Jump_performed;
    }

    private void Jump_performed(UnityEngine.InputSystem.InputAction.CallbackContext obj)
    {
        if (_controller.isGrounded)
        {
            _isJumping = true;
        }
    }

    // Update is called once per frame
    void Update()
    {
        Vector2 playerMovement = _playerInputs.Platforming.Movement.ReadValue<Vector2>();
        playerMovement.Normalize();

        Vector3 velocity = new Vector3(playerMovement.x, 0, 0) * _moveSpeed;

        if (!_controller.isGrounded)
        {
            _yVelocity -= _gravity;
        }
        else
        {
            if (_isJumping)
            {
                _yVelocity = _jumpHeight;
                _isJumping = false;
            }
            else
            {
                _yVelocity = 0;
            }
        }

        velocity.y = _yVelocity;

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