Jumping cancels out x and z velocity.

So Im working on a movement script. Im using addforce for movement so that I can have acceleration, the only problem is that when I jump, my momentum going forward is reset. The bigger problem is that if i jump and try and move forward, my character decelerates until I can't move at all until I land. I need a way so that the jumping carries over the momentum. Here is my code:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class movement : MonoBehaviour
 {
     public Rigidbody rb;
     public Transform cam;
     public float speed = 15f;
     public float maxSpeed = 10f;
     public float gravity = -10f;
     public float jumpPower = 10;
     public float turnSmoothTime = 0.01f;
     float turnSmoothVelocity;
     public Animator anim;
 
     float velocity = 0f;
 
     //ground
     public Transform groundCheck;
     public LayerMask groundMask;
     bool grounded;
 
     //ground comformity
     public Transform objectToPlace;
 
     // Update is called once per frame
     private void Update()
     {
         //hide the cursor
         if (Input.GetMouseButtonDown(2))
         {
             Cursor.visible = false;
         }
 
         grounded = Physics.CheckBox(groundCheck.position, new Vector3(0.4f, 0.2f, 0.4f), rb.rotation, groundMask);
 
         if (Input.GetButtonDown("Jump") && grounded)
         {
             rb.velocity = (new Vector3(0f, jumpPower, 0f));
         }
 
     }
     
     void FixedUpdate()
     {
         //gravity
         rb.AddForce(new Vector3(0f, gravity, 0f));
 
         float xinput = Input.GetAxisRaw("Horizontal");
         float yinput = Input.GetAxisRaw("Vertical");
         Vector3 direction = new Vector3(xinput, 0f, yinput).normalized;
 
         //movement
         if (direction.magnitude >= 0.1f)
         {
             float targetAngle = Mathf.Atan2(direction.x, direction.z) * Mathf.Rad2Deg + cam.eulerAngles.y;
             float angle = Mathf.SmoothDampAngle(transform.eulerAngles.y, targetAngle, ref turnSmoothVelocity, turnSmoothTime);
             rb.rotation = Quaternion.Euler(0f, angle, 0f);
 
             Vector3 moveDir = Quaternion.Euler(0f, targetAngle, 0f) * Vector3.forward;
 
             //this code makes it so that I dont go too fast, and the tempY thing is because the jumpheight was too lower and more floaty when moving
             float tempY = rb.velocity.y;
             if (rb.velocity.magnitude > maxSpeed)
             {
                 rb.velocity = rb.velocity.normalized * maxSpeed;
             }
             rb.velocity = new Vector3(rb.velocity.x, tempY, rb.velocity.z);
 
             //this aplies the movement
             rb.AddForce(moveDir * speed);
 
             //ground comformity
             Ray ray = new Ray(transform.position, -transform.up);
             RaycastHit hitInfo;
             float maxDistance = 1.5f;
 
             if(grounded)
             {
                 maxDistance = 5f;
             }
             
             if (Physics.Raycast(ray, out hitInfo, maxDistance, groundMask))
             {
                 rb.rotation = Quaternion.FromToRotation(Vector3.up, hitInfo.normal) * rb.rotation;
                 Debug.DrawLine(ray.origin, hitInfo.point, Color.red);
             }
             else
             {
                 Debug.DrawLine(ray.origin, ray.origin + ray.direction * 1.5f, Color.green);
             }
         }
 
         //animation
         anim.SetFloat("Speed", Mathf.Abs(direction.x) + Mathf.Abs(direction.z));
         anim.SetBool("Jumpy?", grounded);
     }
 }