Withholding Fatima letters? What Fatima letters, Sr Lucia’s? If that’s the case they’re there on the internet for all to see, not locked away anywhere.
And the gnostic gospels? They’ve all been known of and read fairly widely ever since they were written. Some of them indeed make claims that, if true, are contrary to Christian and Catholic teaching. Doesn’t mean the Church suppressed them, just exposed them for the illogic and nonsense they are.
One example - the Da Vinci Code is based on a few gnostic gospels that have been around since about the third century. These gospels were known and read throughout the land of France for one, and the Kings of France claimed for several centuries to be descended from Christ through Mary Magdalene as a result.
Something known throughout the entire country of France can hardly be said to have been ‘suppressed’ now can it? And if this gnostic gospel, one of the most controversial, wasn’t suppressed, then why suppress any others?