There is no need to have a separate button to show keys. Its just another extra step that takes more time. Have one button that shows everything would be helpful. Ideally having a search function for Prime would be a huge step forward.
Keys are separated everywhere in the app. If you open a Key Capsule it auto-selects keys, however Quantum Capsules are more often used for Items so it selects items by default.
Iirc for the game mechanics, you can unload all of the regular items at once while leaving in keys with a single button (or take all your keys leaving items). This alone is a very handy feature if used that way.
Having a seperate button to show keys everywhere is god-like UX. It means that in the future, Key searching, Key management, Key Selection can be task-specific without getting in the way of the rest of the UI.