I’ve been searching and searching, the devhub/wiki used to have a page or image that showed what buttons on a controller each keycode correspond to. It’s not on the Enum page for keycodes, not on UserInputService page, and of all places it’s not on the article for adding gamepad support to your game.
It was the Wiki. The Developer Hub does not have this page, among a number of other valuable resources that were lost because not all pages were moved before the Wiki was sliced.
The page you are (or rather were) looking for is called Input Image Library. This showcased the library, how to use it and mapped out the inputs for gamepads.
Apparently this page did exist but it was removed? I found a legacy link to it: