My MacBookPro 15" Retina had the same issue when I installed MacOS 11. I didn't plan to but my last beta update for Catalina was corrupt and the only way I could gaing contol was to do a CMD R and reinstall. It chose Big Sur. Since it couldn't identify my WiFi network on retart after install, there was no way to trouble shoot. So I found a Cat5 cable and headed to my router. As soon as plugged in the Cat5 into Thunderbolt adapter, it found everything, connected to Ethernet and WiFi simultaneously. Give that a shot and see if that helps.

Check Feedback Assistant, specifically known issues with Big Sur. You'll find what you're reporting is known issue. Known Issues If you updated to macOS Big Sur 11 beta from a previous version of macOS, Software Update might show "Unable to check for updates - Failed to download the documentation for the minor update. Please try again later". (63158434) Workaround: Start up from macOS Recovery. If your data volume is encrypted, use Disk Utility to mount it. In Terminal type rm -rf "/Volumes/Macintosh HD - Data/private/var/folders/zz/zyxvpxvq6csfxvn_n00000y800007k". Restart your Mac. There is additional data which is helpful. I suggest you review it, since it doesn't apply to everyone. Hope this helps.

I had a similar experience. I restarted the Mac holding down CMD+R and chose "Reinstall MacOS." It worked.