some updates

Assets/songsDatabase/SongDataController/SongSelectUI.cs

@@ -33,6 +33,8 @@ public class SongSelectUI : MonoBehaviour
     // Current DLC key used for per-DLC saved song selection
     public static string CurrentDlcKey = "dlc_default_0";
     public static bool ForceFirstSongOnNextRestore;
+    private const string GlobalSelectedDifficultyPrefsKey = "song_select_global_difficulty";
+    private static int cachedSelectedDifficulty = -1;
 
     // Track pending restore to avoid multiple overlapping restores
     private Coroutine restoreCoroutine;
@@ -72,6 +74,79 @@ public class SongSelectUI : MonoBehaviour
         }
     }
 
+    public static int GetSelectedDifficulty()
+    {
+        if (cachedSelectedDifficulty < 0)
+        {
+            cachedSelectedDifficulty = Mathf.Clamp(PlayerPrefs.GetInt(GlobalSelectedDifficultyPrefsKey, 0), 0, 3);
+        }
+
+        return cachedSelectedDifficulty;
+    }
+
+    public static void SetSelectedDifficulty(int difficulty)
+    {
+        cachedSelectedDifficulty = Mathf.Clamp(difficulty, 0, 3);
+        PlayerPrefs.SetInt(GlobalSelectedDifficultyPrefsKey, cachedSelectedDifficulty);
+        PlayerPrefs.Save();
+    }
+
+    public static void ApplySelectedDifficultyToLoadedSongButtons()
+    {
+        int difficulty = GetSelectedDifficulty();
+        SongButton[] buttons = UnityEngine.Object.FindObjectsByType<SongButton>(FindObjectsInactive.Include, FindObjectsSortMode.None);
+        for (int i = 0; i < buttons.Length; i++)
+        {
+            SongButton button = buttons[i];
+            if (button == null)
+            {
+                continue;
+            }
+
+            SongData song = button.GetAssignedSongData();
+            ApplySelectedDifficultyToSong(song, difficulty, true);
+            button.RefreshCurrentDifficultyDisplay();
+        }
+
+        PlayerPrefs.Save();
+    }
+
+    public static void ApplySelectedDifficultyToSongList(IEnumerable<SongData> songs)
+    {
+        int difficulty = GetSelectedDifficulty();
+        if (songs == null)
+        {
+            return;
+        }
+
+        foreach (SongData song in songs)
+        {
+            ApplySelectedDifficultyToSong(song, difficulty, true);
+        }
+
+        PlayerPrefs.Save();
+    }
+
+    public static void ApplySelectedDifficultyToSong(SongData song)
+    {
+        ApplySelectedDifficultyToSong(song, GetSelectedDifficulty(), true);
+    }
+
+    private static void ApplySelectedDifficultyToSong(SongData song, int difficulty, bool persist)
+    {
+        if (song == null)
+        {
+            return;
+        }
+
+        difficulty = Mathf.Clamp(difficulty, 0, 3);
+        song.thisLevel_selectedDifficultyID = difficulty;
+        if (persist)
+        {
+            PlayerPrefs.SetInt(SongButton.BuildSongSelectedDifficultyPrefsKey(song.songID), difficulty);
+        }
+    }
+
     private void OnDisable()
     {
         KillActiveTweensAndCoroutines();
@@ -180,6 +255,8 @@ public class SongSelectUI : MonoBehaviour
         // allow UI to render a frame before heavy instantiation
         yield return null;
 
+        ApplySelectedDifficultyToSongList(list);
+
         int count = 0;
         foreach (var song in list)
         {
@@ -449,7 +526,7 @@ public class SongSelectUI : MonoBehaviour
 
         TMP_Text[] texts = songButtonObj.GetComponentsInChildren<TMP_Text>();
 
-        if (texts.Length >= 4)
+        if (songButton == null && texts.Length >= 4)
         {
             texts[0].text = song.songName;
             texts[1].text = "Record : " + bestTotal;