The only thing official that I could find is that the Touch ID Magic Keyboard won’t work with the new iPads but only the Touch ID doesn’t work the keyboard itself does. This is the iMac Magic Keyboard.
Touch ID on iMac's Magic Keyboard won't work with iPad Pro | AppleInsider
The Touch ID sensor on the iMac's new Magic Keyboard reportedly won't work with the latest iPad Pro, despite running the same M1 chip powering compatible Macs.
appleinsider.com