I have a first generation 12.9” iPad Pro and just got a Logitech K811 keyboard to use with it. It works great but the brightness keys won’t control the screen brightness. It’s not the keys themselves since I tried the same keyboard on a Mac and it works fine. Anyone else use this combo and successfully able to control brightness?
I have that keyboard and the 10.5”. Unfortunately the brightness keys just do not work and I have to adjust it through control center.
Having the same setup as you, and I can confirm that brightess keys do not work on my iPad Pro 12.9 either. When connected to the iMac, they work perfectly, so I suspect an issue with iOS for this one.