Referencing a script from another script does not work,Referencing functions from another Script isnt working

I am getting more and more frustrated and just can't get to the bottom of this problem I have.I want to call a function from another Script in my "Player"-Script but Unity keeps throwing this error: NullReferenceException: Object reference not set to an instance of an object Player.Start () (at Assets/Scripts/Player.cs:22) I have looked up multiple solutions but none of them seem to work. What is confusing me, is the fact that the functions and the class itself in the "PowerBar"-Script show that they are being referenced in the "Player"-Script. I don't get why Unity tells me that they are not referenced to.

This is the Player-Script: (PlayerMovement is the CharacterController-Script, which works perfectly fine)

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class Player : MonoBehaviour
 {
     public PlayerMovement playerMovement;
     float horMove = 0f;
     bool jump = false;
     bool crouch = false;
     public float runSpeed = 40f;
 
     public PowerBar powerBar;
     public int minPower = 10;
     public int currentPower;
 
 
     // Start is called before the first frame update
     void Start()
     {
         currentPower = minPower;
         powerBar.SetMinPower(minPower);
     }
 
     // Update is called once per frame
     void Update()
     {
         PlayerInput();
         GainPower(10);
     }
 
     void FixedUpdate()
     {
         // Move Character
         playerMovement.Move(horMove * Time.fixedDeltaTime, crouch, jump);
         jump = false;
     }
 
     void PlayerInput()
     {
         horMove = Input.GetAxisRaw("Horizontal") * runSpeed;
 
         if(Input.GetButtonDown("Jump"))
         {
             jump = true;
            }
 
         if(Input.GetButtonDown("Crouch"))
         {
                 crouch = true;
         } else if(Input.GetButtonUp("Crouch"))
            {
               crouch = false;
            }
     }
 
     void GainPower(int gain)
     {
         if(Input.GetKeyDown(KeyCode.Y)) 
         {
             currentPower += gain;
             powerBar.SetPower(currentPower);
         }
     }
 }

This is the PowerBar Script:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.UI;
 
 public class PowerBar : MonoBehaviour
 {
     public Slider slider;
     public Gradient gradient;
     public Image fill;
 
     public void SetMinPower(int power)
     {
         slider.minValue = power;
         slider.value = power;
 
         fill.color = gradient.Evaluate(1f);
     }
     public void SetPower(int power)
     {
         slider.value = power;
 
         fill.color = gradient.Evaluate(slider.normalizedValue);
     }
 }

I hope someone can help me because I spent way too much time on this simple problem. Both of the Scripts are stored in the same folder by the way, so that can't be the problem.