Hello Dano4444,
Thanks for using Apple Support Communities! We see you're having an issue using your iPad Pro with SideCar, and we'd like to help.
It looks like you have gone through the article viewed before posting, which has great info. Did you also happen to check the section titled "Additional requirements"? Here's the article again:
Use an iPad as a second display for a Mac
If everything is as it should be, but still not able to connect to the iPad, we've got some other troubleshooting steps you can try.
On your MacBook Pro:
How to reset the SMC of your Mac
Reset NVRAM or PRAM on your Mac
On your iPad Pro:
Reset your Network Settings.
Go to Settings > General > Reset > Reset Network Settings. This also resets Wi-Fi networks and passwords, cellular settings, and VPN and APN settings that you've used before.
Try connecting again, and hopefully that will work.
Cheers!