Last night I upgraded from iPadOS 15 public beta 3 to public beta 4. This morning, I go to put my iPad onto my Apple Magic Keyboard and it worked for about five seconds, and then a popup came up that says "Accessory Not Supported - This accessory is not supported by this device."
Now, my iPad continues to charge on the keyboard, but I can't use the actual keyboard or the trackpad at all.
If I take the iPad off and put it back on, I get the same result ... works for about five seconds, then the popup comes up again.
Ideas?