Hey I know this is super old but I'm using binary files to save. Does this look like roughly what you got working? I'm still having some trouble with this.
public void SaveGameStats()
{
string saveFileName = "GameStats";
string savePath = Application.persistentDataPath;
#if UNITY_WEBGL
savePath = "idbfs/Skull_Scavenger";
#endif
using (FileStream file = File.Create(Path.Combine(savePath, saveFileName)))
{
new BinaryFormatter().Serialize(file, curGameStats);
}
}