Setting the max velocity of a rigidbody

Trying to set the velocity of a RigidBody and add force doesn't always play nice together. As described by this stackexchange post, you probably want to avoid capping the speed by setting velocity -- instead, simply stop adding force when the speed limit is reached. In your game, that would look something like the code below:

 {
     public Transform tr;
     public Rigidbody rb;
     public float maxspeed = 500f;
     public float speed = 450f;
     public float jumpspeed = 600f;
     public GameObject player;
     public bool grounded;
     public GameObject Ground;
     public Animation disappear;
     
     public void Start()
     {
         grounded = true;
     }
 
     public void OnCollisionEnter(Collision theCollision)
     {
         if (theCollision.gameObject.name == "Ground")
         {
             grounded = true;
         }
     }
 
     public void OnCollisionExit(Collision theCollision)
     {
         if (theCollision.gameObject.name == "Ground")
         {
             grounded = false;
         }
     }
 
     private void FixedUpdate()
     {
         if (Input.GetKeyDown("e"))
         {   
             disappear["disappear"].speed = 1;
             disappear.Play("disappear");
         }
         if (Input.GetKeyUp("e"))
         {
             disappear["disappear"].speed = -1;
             disappear["disappear"].time = disappear["disappear"].length;
             disappear.Play("disappear");
         }
 
         // only allow adding additional force when the speed is less than the maximum
         if (rb.velocity.magnitude < maxspeed)
         {
             if (Input.GetKey("w") && grounded == true)
             {
                 rb.AddForce(0, jumpspeed * Time.deltaTime,0);
             }
             if (Input.GetKey("a") && grounded == true)
             {
                 rb.AddForce(-speed * Time.deltaTime,0,0);
             }
             if (Input.GetKey("d") && grounded == true)
             {
                 rb.AddForce(speed * Time.deltaTime,0,0);
             }
         }
     }
 }

@Alanisaac Thank you very much for your help i'll test the code later today!