Try this:
Connect your iPad to your iMac/MBP/MB/etc using a lightning cable.
Open Finder, click on your iPad's name.
Click Trust on the iMac/MBP/MB/etc
Tap Trust this Computer on your iPad and enter your PIN as required.
Open the Sidecar preference pane.
Your iPad should be available as a Sidecar device.
paulbeda
Users receive reputation points by contributing quality content to the forums.
Posts include post and replies published on the forums.
Post authors can mark replies as Accepted to indicate successful solutions.
Apple Developer Forums admins can mark replies as Apple Recommended to indicate an approved solution