I was getting so frustrated with this issue too. It worked when connected together with the USB-C cable, but not with Sidecar or Airplay. Somehow I just managed to get my iPad (Pro) to finally show up on my MacBook Pro (macOS Big Sur 11.0.1)! 1) Restart Macbook 2) On iPad, go to Bluetooth Settings, click on MacBook Pro, and then Forget Device 3) On Macbook, go to Bluetooth Settings and remove the iPad by clicking the x on the right side when you hover over iPad. iPad will disappear from the Devices list, but should shortly reappear with the “Connect” button 5) On iPad Bluetooth Settings, your MacBook Pro should also now show up under Other Devices. Click on it, and you should get a Connection Request pop up on your MacBook Pro. Click Connect. 6) iPad should now show up available to connect using either: Display options from the Menu Bar Sidecar Preferences or Display Preferences Good luck!!

I was getting so frustrated with this issue too. But I somehow managed to get my iPad (Pro) to finally show up on my MacBook Pro (macOS Big Sur 11.0.1)! 1) Restart Macbook 2) On iPad, go to Bluetooth Settings, click on MacBook Pro, and then Forget Device 3) On Macbook, go to Bluetooth Settings and remove the iPad by clicking the x on the right side when you hover over iPad. iPad will disappear from the Devices list, but should shortly reappear with the “Connect” button 5) On iPad Bluetooth Settings, your MacBook Pro should also now show up under Other Devices. Click on it, and you should get a Connection Request pop up on your MacBook Pro. Click Connect. 6) iPad should now show up available to connect using either: Display options from the Menu Bar Sidecar Preferences or Display Preferences Good luck!!