Hello Mortt,
Sidecar is a great feature and it sounds as though you've reviewed the following article to verify the system requirements and ensuring Sidecar is set up properly.
Use an iPad as a second display for a Mac
If so, we'll need to isolate the issue further to ensure the right steps are taken from here to reach a resolution. If you haven't already, create a test admin user account on your Mac and log in to that user to see if Sidecar works as expected. You can find the steps for creating a test admin user account listed below.
- Click the Apple logo towards the top-left, followed by System Preferences
- Click Users & Groups.
- Click the padlock icon, then enter the current admin user account login information.
- Once unlocked, click the (+) and follow the prompts to create a new admin user.
- After the test user is created, click the Apple logo towards the top-left.
- Then click Log Out [current user].
- Sign in to the test user, and see if Sidecar works as expected.
Let us know the results!