As far as I know, Sidecar can be used both wirelessly and with a wired connection.
Using Sidecar wirelessly severely cuts my internet connection down from 22Mbps to 4Mbps(both download and upload speed). I am looking for a way to force Sidecar connection to wired connection, using USB-C to USB-C cable. This solution didn't work for me, as when I turn iPad's wifi off and try to connect via Sidecar from Mac, it says:
Sidecar can’t connect wirelessly because your iPad’s Wi‑Fi is not available. To use Sidecar wirelessly, turn on Wi‑Fi and make sure it is not in use for Personal Hotspot.
I'm using Macbook Pro 15'' 2017 with iPad Pro 11'' 2017, Both in latest OS.