On my 2017 12" MacBook, I can't get Sidecar working at all with my 10.5" iPad Pro. Public Beta 1 of Catalina and iPadOS respectively.
The MacBook sees the iPad Pro, but can't connect to it. It says it times out. I've tried WiFi, Bluetooth, and wired. None work.
It's kinda moot though, since it looks like I won't be able to run Catalina anyway for a while. Neither of my two different VPN software packages that I use for my two workplaces work in Catalina (or iPad OS for that matter).