Simple solve! I was having a similar issue, and it turned out that my iPad had (for no reason at all) disconnected from my wifi network. I went into settings and selected my home wifi from the list of networks and it connected immediately. I have no clue why it wasn't automatically connected to my wifi, since I was using it 12 hours ago in the exact same location, with the exact same setup - usb-c connection to Macbook Pro - with a perfect sidecar connection. 🤷‍♂️