What were the big sins of St Peter that the Vatican tried to hide from the world?

Answer 1

You're presuming that there are such, which may not be warranted.

Peter was often called "the apostle with the foot-shaped mouth", and several of his failings are illuminated for all to see within the gospels and the book of Acts. If the Vatican is trying to hide these from the world, they're doing a spectacularly bad job of it, and one might suggest that putting them in black and white in your own holy book is a singularly odd way of attempting to hide something.

However, we have very little historical data on Simon-called-Peter, and any supposed "big sins" would be as poorly attributed as other data like, for example, the name of his wife. The burden of proof would be on anyone claiming that he had "big sins", and there simply is no proof of any beyond those explictly or implicitly set out in scripture.