A new external screen
Apple already has the Pro Display XDR, but that is priceless for many people. The upcoming new screen could well fall in the same price range. According to sources, Apple is internally testing a new external display with its own A13 chip and a Neural Engine, just like in the iPhone 11 series. Other technical specs are not yet known. It is being developed under the code name J327.
Thanks to the Neural Engine, the screen would be extra suitable for machine learning tasks. It sounds a lot more advanced than the Thunderbolt Display, which Apple discontinued in 2016. Shortly afterwards, rumors arose that Apple would be working on a successor with a built-in GPU. That is not yet in the Pro Display XDR, but it could be part of the upcoming screen.
A proprietary CPU and GPU in the display can provide better high-resolution graphics, with less stress on the computer's internal chip. Apple could also combine the power of both processors for extra demanding tasks.