It’s apostasy; but it’s no secret.
After all, you knew about it.
However, the likely reason for the apostasy is that they’ve gone beyond the Bible. The institution has vaults of many square miles of knowledge that they don’t let the world know about. You know this as well as I do. The Church is 1700 years old, if you count from the time of Constantine and they’ve been gathering knowkedge in all that time.