Apps · The Apps window and launcher
Why is one of my apps missing from the Apps window?
Short answer: It may live outside the folders Storage Studio scans (Applications, your personal Applications folder, Setapp, Utilities), or the Older than / Hide running filters are hiding it.
Usually it's installed somewhere Storage Studio doesn't scan, or it's being filtered out. Storage Studio looks in the main Applications folder, your personal Applications folder, Setapp and Utilities; an app kept in another folder (for example on the Desktop or inside a downloads folder) won't appear.
On the Internal tab, also check the Older than filter and Hide running. Apple's built-in system apps are never listed for moving.