“Secret Menus” aren’t a real thing. It’s just a way people refer to ordering off-menu. For example, Starbucks has a blended strawberry drink, and they have chocolate chips. There is no chocolate chip blended strawberry drink on the menu, but you can order the blended strawberry drink and ask for them to put chocolate chips in it, and they will sell that to you (probably at a small upcharge compared to ordering it without the chocolate chips). That doesn’t mean there’s an actual special other menu they don’t tell you about that has a chocolate chip blended strawberry drink on it. They just can’t list every possible combination of their interests on their menu. But they’ll sell you whatever combination you ask for, because they want your money. Calling it a secret menu is frankly kind of disingenuous and misleading, but it is catchy, so it’s stuck around.