N. Ingraham, writing at Engadget:
Apple is making Stage Manager work with a number of older devices: it’ll work on the 11-inch iPad Pro (first generation and later) and the 12.9-inch iPad Pro (third generation and later). Specifically, it’ll be available on the 2018 and 2020 models that use the A12X and A12Z chips rather than just the M1. However, there is one notable missing feature for the older iPad Pro models — Stage Manager will only work on the iPad’s build-in display. You won’t be able to extend your display to an external monitor.
Apple also says that developer beta 5 of iPadOS 16 is removing external display support for Stage Manager on M1 iPads, something that has been present since the first iPadOS 16 beta was released a few months ago. It’ll be re-introduced in a software update coming later this year.
I’m glad Apple found a way to support older iPads with this feature, but pulling external display support for M1 iPads running Stage Manager is curious. Clearly Apple is doing what it can to get this out the door.