Last week, Apple introduced a brand new iPad Pro with a 12.9-inch XDR display. Due to the new display technology, the Magic Keyboard from 2020 is said to not be a perfect fit. Now Apple has spoken out.
In a new support document released today, Apple has clarified the situation surrounding the Magic Keyboard's compatibility with the new 12.9-inch iPad Pro. The company now says that the first-generation Magic Keyboard is "functionally compatible" with the new 12.9-inch iPad Pro. There is a catch, however. It may not "fit snugly when closed." The new iPad Pro is 0.5mm thicker than its predecessor due to the new mini-LED display technology. As Apple explains, this difference in thickness is the reason why the 12.9-inch iPad Pro doesn't fit perfectly into the old Magic Keyboard.

iPad Pro 12.9″ XDR: Magic Keyboard “is functionally compatible”
The company also warns that screen protectors could further affect the fit. support document:
The first generation Magic Keyboard (A1998) is functionally compatible with the new iPad Pro 12.9-inch (5th generation) with Liquid Retina XDR display. Due to the slightly thicker dimensions of this new iPad Pro, it is possible that the Magic Keyboard may not fit snugly when closed, especially with screen protectors applied.
Previously, reports suggested that the first-generation 12.9-inch Magic Keyboard with model number A1998 would not work with the new fifth-generation 12.9-inch iPad Pro. This issue now seems to have been resolved. (Photo by Elinaxx1v / Bigstockphoto)