I have the 2017 MacBook Core m3 and 2017 iPad Pro 10.5". Both officially support Sidecar.
With Public Beta 1 on both machines, sometimes I can see the iPad Pro for Sidecar, but can't connect to it.
With Public Beta 2 on both machines, sometimes I can see the iPad Pro for Sidecar, but can't connect to it.
If I pair the machines via Bluetooth, but using only WiFi connecting via cellular through my phone for my iCloud login, I can't even see the iPad Pro for Sidecar. It seems the best I can get is with a wired Lightning connection, but all that does is give me the Sidecar icon. When I try to connect, it just times out. Not sure why trying to connect Sidecar is so complicated. I would have thought physically plugging in the iPad Pro would make Sidecar a simple process, but no such luck.
Anyhow, here's hoping for iPadOS 13 PB3 and macOS 10.15 Catalina PB3.