According to information provided by Apple to Engadget.
The beta also removes Stage Manager external display support for the time being, with the feature set to return in a later iPadOS 16 update. Apple’s statement on this:
We introduced Stage Manager as a whole new way to multitask with resizable overlapping windows on both the iPad screen and a separate external display, with the ability to run up to to eight live apps on screen at once. Providing this multi-screen support is only possible with the full power of M1-based iPads. Customers with 3rd and 4th generation iPad Pros have expressed strong interest in being able to experience Stage Manager on their iPads. In response, our teams worked hard to find a way to provide a single-screen version for these systems, with simultaneous support for up to four live apps on the iPad screen.
External display support for Stage Manager on M1 iPads will be available in a software update later this year.
During the iPadOS 16 beta testing period, Stage Manager was limited to the M1 iPad Pro models released in 2021 and the iPad Air M1. All other iPads were unable to use this feature, including the 2018 and 2020 iPad Pro models which use the A12X and A12Z chips. Apple argued that it was unable to deliver acceptable performance on non-M1 iPads because the feature requires “large internal memory, incredibly fast storage, and flexible external display I/O” provided by M1 iPad models.
Apple was reportedly unhappy with the Stage Manager experience on older iPad Pro models. “Certainly, we would like to bring a new experience to every device that we can, but we also don’t want to hold back the definition of a new experience and not create the best foundation for the future in that experience. And we could really only do this by relying on the M1,” Apple’s Craig Federighi said.
Apple received constant criticism for limiting such an important feature to its newer hardware, leading the company to find a way to extend the feature to other iPads. Removing the external display feature in Stage Manager may be what allows Apple to deliver a proper experience on non-M1 hardware, but when external display support is reintroduced it will be limited to M1 iPad models and will not be available on 2018 and 2020 iPad.
Stage Manager is now available on all M1 iPads as well as the 11-inch and 12.9-inch iPad Pro models from 2018 and 2020, as long as the latest iPadOS 16.1 beta is installed. Note that Apple calls this beta iPadOS 16 beta 10.