Ok so I had the same problem my WiFi was connected but not working as I checked on the network page in system preferences, I also tried to plug in a either net cable directly and exactly the same issue it was showing as connected but not getting internet. i tried all the suggestions here in the chat but no luck, I then realised that I saw somewhere that you need to disconnect your VPN and just before this issue happened I was trying to use my VPN but did not make the connection at the time. not sure if there is a bug in Big Sur that has issues with VPNs but it seems this was the issue, my VPN was constantly trying to connect with no luck but as it’s truly oh to connect it’s on a constant loop so this was blocking the internet while looping. so I went to System Preferences > then in the list I clicked on VPN and I could see it was trying to constantly connect so I could not disconnect it from there. so I opened up Finder and click on the applications folder and deleted my VPN application there, as soon as I did this the internet stringed to life and it’s all working ok. hope this works for others as it’s super worrying when this issue occurs, it must be some sort of bug in big sur or something