How do I save a list of scriptable objects?

I tried following a tutorial on saving scriptable objects, and changing the script a bit to save a list of scriptable objects, and it's not working for me. I literally can't find ANYTHING on saving lists of scriptable objects. Does anybody know what I'm doing wrong?

 public class ScriptableObjectSave : MonoBehaviour
 {
     public static ScriptableObjectSave instance;
 
     public Item item;
 
     public List<Item> items;
     [SerializeField] Inventory inventory;
 
 
     void Awake()
     {
         if(instance == null)
         {
             instance = this;
         }
         else if(instance != this)
         {
             Destroy(this);
         }
         DontDestroyOnLoad(this);
     }
 
     private void Start()
     {
         
     }
 
     public bool IsSaveFile()
     {
         return Directory.Exists(Application.persistentDataPath + "/SO_save");
     }
 
     public void SaveGame()
     {
         items = inventory.items;
 
         if (!IsSaveFile())
         {
             Directory.CreateDirectory(Application.persistentDataPath + "/SO_save");
         }
         if(!Directory.Exists(Application.persistentDataPath + "/SO_save/character_data"))
         {
             Directory.CreateDirectory(Application.persistentDataPath + "/SO_save/character_data");
         }
         BinaryFormatter bf = new BinaryFormatter();
         FileStream file = File.Create(Application.persistentDataPath + "/SO_save/character_data/character_save.txt");
         var json = JsonUtility.ToJson(items);
         bf.Serialize(file, json);
         file.Close();
     }
 
     public void LoadGame()
     {
         if(!Directory.Exists(Application.persistentDataPath + "/SO_save/character_data"))
         {
             Directory.CreateDirectory(Application.persistentDataPath + "/SO_save/character_data");
         }
         BinaryFormatter bf = new BinaryFormatter();
         if(File.Exists(Application.persistentDataPath + "/SO_save/character_data/character_save.txt"))
         {
             FileStream file = File.Open(Application.persistentDataPath + "/SO_save/character_data/character_save.txt", FileMode.Open);
             JsonUtility.FromJsonOverwrite((string)bf.Deserialize(file), items);
             file.Close();
         }
 
         inventory.items = items;
     }