How do you save decimals with PlayerPrefs using XML???

You can't save decimal numbers.

So instead you will have to save it as a string.

Use decimal.tryParse() and myDecimal.toString()

You can use decimal.parse() if you are sure you will not get an exception.

You can writer a wrapper:

 public static class PlayerPrefsWrapper
 {
 
  public static void SetDecimal(string key, decimal value)
  {
       PlayerPrefs.SetString(key, x.ToString());
  }
 
  public static decimal GetDecimal(string key)
  {
        decimal value;
        return PlayerPrefs.HasKey(key) && Decimal.TryParse(PlayerPrefs.GetString(key), out value) ? value : 0;
  }
 
 }

then in your savestate class you just have to do:
Set: PlayerPrefsWrapper.SetDecimal("bitcoin", bitcoin); Get: bitcoin = PlayerPrefsWrapper.GetDecimal("bitcoin");