The model is opt-out, not opt-in: compatible iPad and iPhone apps are listed in the Vision Pro App Store by default, and a developer can exclude their app in App Store Connect. Some categories are never listed — notably the Kids category.
What works well: productivity and media apps (word processors, note apps, browsers, streaming) generally feel fine, since they're essentially floating iPad windows. What's limited: apps that rely on motion, phone sensors (pedometers, some ARKit titles), or exact touch precision behave awkwardly or are excluded by developers for that reason. Games run, but often without the polish of native titles.
Telling them apart: in the App Store on Vision Pro, filter 'Apple Vision Apps' for native ones; iPad/iPhone apps appear under 'iPhone & iPad Apps' and run in a compatibility window. Native apps support spatial features (3D objects, hand tracking); adapted apps are flat windows.
In practice: assume an adapted iPad app works 'well enough' until proven otherwise, and prefer native versions for anything central to your workflow.
Sources: https://developer.apple.com/visionos/submit/
— Osnivo Editorial