Time.deltaTime/Time.fixedDeltaTime are messing with gravity

I am moving a cube by changing the velocity of its rigidbody directly in fixed update, but it fell very slowly when in the air. I found out that it was caused by multiplying the intended velocity by Time.deltaTime in fixed update. I googled it, and apparently Time.fixedDeltaTime is supposed to be for fixed update, but when I tried it, that same problem occurred. When I don't use either, there are no problems. While not using Time.deltaTime or Time.fixedDeltaTime cause problems with different frame rates, and if so, how do I use them without affecting the speed of falling? Edit: Solved. I realize that I don't need to use Time.deltaTime or Time.fixedDeltaTime when changing the velocity directly.

 public class PlayerCamManager : MonoBehaviour
 {
     public Camera playerCamera;
     public GameObject playerCharacter;
     public Transform camContainer;
     public Transform camContainerTwo;
     public Vector3 camStartingPos;
     Rigidbody rb;
     Vector3 camContainerTwoRotation;
     Vector3 camContainerRotation;
     Vector3 finalMovement;
     public float moveSpeed;
     public float lerpSpeed;
     float xInput;
     float zInput;
 
     void Awake()
     {
         camContainer.SetParent(camContainerTwo);
         camContainer.localPosition = new Vector3(0, 0, 0);
         playerCamera.transform.SetParent(camContainer);
         playerCamera.transform.localPosition = camStartingPos;
         rb = playerCharacter.GetComponent<Rigidbody>();
     }
     
     void Update()
     {
         Vector3 input = new Vector3(Input.GetAxis("Horizontal"), 0, Input.GetAxis("Vertical"));
         float h = moveSpeed;
         float a = playerCharacter.transform.rotation.eulerAngles.y;
         a = a * Mathf.Deg2Rad;
         if (input.x != 0)
         {
             if (input.x > 0)
             {
                 float i = Mathf.LerpAngle(playerCharacter.transform.rotation.eulerAngles.y, camContainerTwo.rotation.eulerAngles.y + 90, lerpSpeed * Time.deltaTime);
                 playerCharacter.transform.eulerAngles = new Vector3(0, i, 0);
             }
             else
             {
                 float i = Mathf.LerpAngle(playerCharacter.transform.rotation.eulerAngles.y, camContainerTwo.rotation.eulerAngles.y - 90, lerpSpeed * Time.deltaTime);
                 playerCharacter.transform.eulerAngles = new Vector3(0, i, 0);
             }
             float xInput = (h * Mathf.Sin(a));
             float zInput = (h * Mathf.Cos(a));
             Vector3 moveDirection = new Vector3(xInput, 0, zInput);
             finalMovement = moveDirection;
             return;
         }
         else if (input.z != 0)
         {
             float i = Mathf.LerpAngle(playerCharacter.transform.rotation.eulerAngles.y, camContainerTwo.rotation.eulerAngles.y, lerpSpeed * Time.deltaTime);
             playerCharacter.transform.eulerAngles = new Vector3(0, i, 0);
             float xInput = (h * Mathf.Sin(a));
             float zInput = (h * Mathf.Cos(a));
             Vector3 moveDirection = new Vector3(xInput, 0, zInput);
             finalMovement = moveDirection * input.z;
             return;
         }
         else
         {
             finalMovement = new Vector3(0, 0, 0);
         }
     }
 
     void FixedUpdate()
     {
         finalMovement.y = rb.velocity.y;
         rb.velocity = finalMovement * Time.fixedDeltaTime;
     }
     void LateUpdate()
     {
         camContainerTwo.position = playerCharacter.transform.position;
         camContainerTwoRotation.y = camContainerTwoRotation.y + (Input.GetAxis("Mouse X") * Time.deltaTime * 180);
         camContainerRotation.x = camContainerRotation.x - (Input.GetAxis("Mouse Y") * Time.deltaTime * 180);
         if (camContainerRotation.x < -25)
         {
             camContainerRotation.x = -25;
         }
         else if (camContainerRotation.x > 55)
         {
             camContainerRotation.x = 55;
         }
         camContainerTwo.eulerAngles = camContainerTwoRotation;
         camContainer.localEulerAngles = camContainerRotation;
         playerCamera.transform.LookAt(camContainer.transform.position);
     }
 }