It goes back to ritualistic belief verging upon Gnosticism regarding the “keys of heaven” and Peter. From what I can tell RC’s seem to think it’s a physical object imbued with some sort of magical power. If you need a key then an abracadabra password isn’t far-fetched but it’s straight out of Harry Potter. Par for the course if so.
You can't really "tell" very much, can you? You won't find any discussion of "physical objects" imbued with magical power in the catechism. The "keys" are a symbol of dynastic authority taken straight from Isaiah 22:22, not a physical object.
I have been a Catholic for 66 years. I used to travel extensively, I have read hundreds of books and met thousands of Catholics, and I have never met one --- not one --- who held such a belief, nor have I heard of such a thing until 2 minutes ago when I read what you wrote.
Name one Catholic who believes your "physical object" nonsense.
Or concede that your statement has no foundation.
There is one other option. You said "RCs" believe this. Perhaps you're referring to yourself, RegulatorCountry?