Where is the entry point to the 2023 theme?

I am having an issue with a health system I am making for my game. I have been at it for 3 days now and have not made much progress. For reference, I am following this tutorial by code monkey: Code Monkey Health Tutorial. The goal is to have two buttons, one for healing and one to damage the player, and a Text Mesh Pro UI Text to show the health of the player, just for testing purposes. Unlike the tutorial, the buttons and text are just on a canvas, not attached to the player, as I am setting it up as a form of a HUD system. also, forgive the formatting, during troubleshooting, I was more focused on trying to fix my issue and my code became a bit of a mess. Sorry for that.

I have three scripts

    using UnityEngine;


    public class HealthSystem
    {
        private int _health;
        private int _healthMax;

        public HealthSystem(int healthMax)
        {
            this._healthMax = healthMax;
            _health = healthMax;
            Debug.Log("healthSystem Created");
        }
        public int GetHealth()
        {
            return _health;
        }
        public void Damage(int damageAmount)
        {
            _health -= damageAmount;
            if (_health < 0) _health = 0;
        }
        public void Heal(int healAmount)
        {
            _health += healAmount;
            if (_health > _healthMax) _health = _healthMax;
        }
    }

    using UnityEngine;

    public class GameHandler : MonoBehaviour
    {
        private HealthButtons _healthButtons;

        private void Start()
        {
            HealthSystem _healthSystem = new HealthSystem(100);
            Debug.Log("Health = "+_healthSystem.GetHealth());
            _healthButtons.Setup(_healthSystem);
        }
    }
}

using UnityEngine;
using TMPro;


    public class HealthButtons : MonoBehaviour
    {
        [SerializeField]
        private TextMeshProUGUI numberText;
        private static HealthSystem _healthSystem;
        private int intToStringHealth;


        public void DamageButton()
        {
            _healthSystem.Damage(10);
            Debug.Log(_healthSystem.GetHealth());
        }
        public void HealButton()
        {
            _healthSystem.Heal(10);
            Debug.Log(_healthSystem.GetHealth());
        }
        public void Setup(HealthSystem healthSystem)
        {
            if (healthSystem == null) Debug.Log("healthSystem");
            Debug.Log(healthSystem);
            _healthSystem = healthSystem;
            Debug.Log("Setup is running");
        }
        private void Update()
        {
            intToStringHealth = _healthSystem.GetHealth();
            numberText.text = intToStringHealth.ToString();
        }
    }

my issue currently is Im trying to create an instance of HealthSystem in GameHandler, which I am successful in, then pass the information to HealthButtons using _healthButtons.Setup(). This is where I become unsuccessful as I am getting a NullReferenceException error.

from my efforts of troubleshooting currently, I have determined I am not calling the instance correctly, but I do not want to use code monkey’s libraries. I have tried making all classes monoclasses and attaching them to game objects and using SerializeFields for all my variables, which does work, but I am not sure that is best practice as I do know linking everything up in the inspector can be a chore if something goes wrong.

This tells me the solution should be fairly simple, I am just not able to articulate the question into google to get the correct answer. It may be a bit overkill just to test a function, but I would like to understand what I am doing wrong and get better. Thank you very much for your help.

I am creating a server authoritative game that uses a public game service API to manage player specific data in the game. The client will authenticate with the auth server, get a token, then use that token to access player specific data in the API. This works well if the API calls to the game services occur on the game client. However, in a server authoritative model, the game server itself would need to make those calls on behalf of the client. My current idea is to replicate the access token to the server and then have the server figure out which token to use when it is requesting data for a specific client. I was curious if this is the best way to do this or is there another approach I should be considering?