Binary save file doesn't seem to be in binary?

I recently wrote a pretty simple save system following a youtube tutorial, which is supposed to save the file in binary and make it hard to edit so players can't just edit their save data easily, however this is how the save file looks when opened in notepad:

 
   ÿÿÿÿ
          FAssembly-CSharp, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null
   
 PlayerData
   
 playerName
       Evelyn

As you can see, it would be pretty easy to edit the name there, and it's obvious what the field is referencing. Did I do something wrong in my code to make it be serialized this way?

Here is my code:

Player.cs:

 using UnityEngine;
 using TMPro;
 public class Player : MonoBehaviour
 {
     public string playerName;
     public TextMeshProUGUI nameDisplay;
 
     private void Awake()
     {
         nameDisplay.text = playerName;
     }
     public void SavePlayer()
     {
         SaveSystem.SavePlayer(this);
         Debug.Log("Saved: " + playerName);
     }
 
     public void LoadPlayer ()
     {
         PlayerData data = SaveSystem.LoadPlayer();
         Debug.Log("Loaded");
 
         playerName = data.playerName;
         nameDisplay.text = playerName;
     }
 }

PlayerData.cs:

 [System.Serializable]
 public class PlayerData
 {
     public string playerName;
 
     public PlayerData (Player player)
     {
         playerName = player.playerName;
     }
 }

SaveSystem.cs:

 using UnityEngine;
 using System.IO;
 using System.Runtime.Serialization.Formatters.Binary;
 
 public static class SaveSystem
 {
     public static void SavePlayer (Player player)
     {
         BinaryFormatter formatter = new BinaryFormatter();
         string path = Application.persistentDataPath + "player.cozy";
         FileStream stream = new FileStream(path, FileMode.Create);
         PlayerData data = new PlayerData(player);
 
         formatter.Serialize(stream, data);
         stream.Close();
     }
 
     public static PlayerData LoadPlayer()
     {
         string path = Application.persistentDataPath + "player.cozy";
         if (File.Exists(path))
         {
             BinaryFormatter formatter = new BinaryFormatter();
             FileStream stream = new FileStream(path, FileMode.Open);
 
             PlayerData data = formatter.Deserialize(stream) as PlayerData;
             stream.Close();
 
             return data;
         }
         else
         {
             Debug.LogError("Save file not found in " + path);
             return null;
         }
     }
 }