Don't even try using an old iPad Pro magnetic stand with the new models because they won't work, the iPad will slip, and so you could even damage your new device.
An older iPad Pro firmly gripped by magnets in a stand
It isn't as if the risk of damage to your new iPad Pro is great, but even the new, stronger design is vulnerable at the corners. So if you did try mounting the new iPad Pro on a stand built for the old one, it will fall and it will likely strike the desk or ground on one of those edges.
The reason you can't use that expensive old stand is down to the redesign of the iPad Pro and ultimately because of how much thinner it is than its predecessor. But this is not like when Apple released the last version of the iPad Pro in 2021.
Back then, the company also released an updated Magic Keyboard and stand, but said that the previous one could still be used with the new iPad Pro. Specifically, Apple said that it was fine, but may not "precisely fit when closed."
In that case, the issue was solely because of the reduced width difference between the 2021 iPad Pro and its 2020 predecessor. This time, width is a straight issue, but there's more to it.
In order to make the new iPad Pro as thin as it is, Apple has redesigned the interior -- and that has included making changes to the magnets inside. The new magnets are bigger and stronger, but they are also positioned sufficiently differently that existing iPad Pro stands won't work.
New iPad Pro stands are coming from third-party accessory makers, and we have a few on the way. In the meantime, some of the latest cases for it include some ability to mount the new device safely.
Leaks about a product can say a lot about what's coming. Accessory manufacturers rely on them to have gear available at launch.
What they don't generally reveal, is magnet positioning.