Personally I am surprised that IPad has its own OS. I thought it uses the same one as iPhone.
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On the contrary, mostly the iPad and iPad OS was the testbed for VisionOS UI management for years, ensuring that iPad apps (and app devs) had to implement support for arbitrary window shapes and layering, using the same affordances (more or less) as VisionOS, unlike iPhone apps that are stuck in portrait or landscape.
There's a lot of truth to AVP is an iPad strapped to your face, and if you have worked on iPad as professional daily driver for 5+ years and now own an AVP, you can remember aspects of VisionPro getting tested in the field over this time period.