I had the problem of MacOS showing connection (both wifi and via ethernet) but no outwards or inwards data were coming in. This was in the official release of Big Sur.
Upgrade from Catalina to Big Sur in a MacBook Pro 2015 15". Eventually the problem is that of incompatible kext (kernel extensions, i.e. module extensions).
Execute in a terminal:
kext | grep -v com.apple
this will show you all the third party kernel extensions (not issued by apple but by third party applications).
The problematic kexts could be VPN software or antivirus software.
In my case it was the Global Protect VPN client installed kexts. The software would not allow me to delete it completely (move to bin) so I had to unload its running kexts and reboot:
launchctl unload /Library/LaunchAgents/com.paloaltonetworks.*
That solved the problem after wasting 2 days!
Check for the other third party kexts (antivirus?) if the VPN is not your problem.
Cheers!
ddracopo
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