How can I make my 2D sprite move in the direction of the most recent key pressed?

 public int a;
 
 void Update ()
      {
          Vector2 movement_vector = new Vector2(Input.GetAxisRaw("Horizontal"), Input.GetAxisRaw("Vertical"));
   
          if (movement_vector == Vector2.up)
          {
             a = 1;
          }
          else if (movement_vector == Vector2.down)
          {
              a = 2; 
          }
          else if (movement_vector == Vector2.left)
          {
              a = 3;   
          }
          else if (movement_vector == Vector2.right)
          {
              a = 4;
           }
          else if (movement_vector == Vector2.zero)
          {
              a = 0; 
          }
      }
  }
 if (a == 1) {
              anim.SetBool("isWalking", true);
              anim.SetFloat("input_x", movement_vector.x);
              rbody.MovePosition(rbody.position + Vector2.up * Time.deltaTime);
 }
 if (a == 2) {
              anim.SetBool("isWalking", true);
              anim.SetFloat("input_x", movement_vector.x);
              rbody.MovePosition(rbody.position + Vector2.down * Time.deltaTime);
 }
 if (a == 3) {
              anim.SetBool("isWalking", true);
              anim.SetFloat("input_x", movement_vector.x);
              rbody.MovePosition(rbody.position + Vector2.left * Time.deltaTime);
 }
 if (a == 4) {
              anim.SetBool("isWalking", true);
              anim.SetFloat("input_x", movement_vector.x);
              rbody.MovePosition(rbody.position + Vector2.right * Time.deltaTime);
 }
 if (a == 0) {
     anim.SetBool("isWalking", false);
 }

I haven't tested it but that should do exactly what you need. It looks bulky but it should work. Basically just creating a new variable that will act as a switch, so that when you hit two keys at once, the most recent will be stored by the a variable, and then acted on accordingly.