All apps on both iOS and iPadOS (as well as all UIs in the OS itself) should be required to support both portrait and landscape orientation. People switch in and out of apps and UIs on these devices constantly. It’s very jarring and annoying seeing a sideways UI when switching between UIs that only support one or the other orientation and having to rotate each time—or worse, apps that force you to rotate the device within the app itself, like video streaming apps that have a portrait-only main UI and landscape-only video player. It’s annoying enough rotating the device when you’re holding it, but people often put these devices on stands and mounts which makes it even more of a chore taking the devices off to rotate them. It’s a terrible UX. Granted some apps are more ideal in one orientation over the other, but I have yet to see an app that would be unusable in either orientation, and it would be a far better UX than constant rotating.