I am having the same issues. I am running Big Sur beta 20A5364e on a late 2019 16" MacBook Pro. I tried using two iPad Pros that previously worked and getting the connection timeout on both devices. I tried the following to no resolve.
Using different Wi-Fi networks
Connecting to USB-C directly with Wi-Fi turned off
Hope this is resolved soon. Using an iPad with Sidecar has been a productivity boost with remote working.
jasonmeans
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