I also experienced no internet after upgrading to Big Sur OS. The earlier post by @axolotl solved the issue for me: "follow the steps on this post apple.stackexchange.com/questions/284581/wipe-all-wifi-settings-from-macbook" (thanks, @axolotl)

::UPDATE:: Well, this seems to have been a temporary solution because I'm no longer able to get back on the internet. WTH APPLE!!! I also experienced no internet after upgrading to Big Sur OS. The earlier post by @axolotl solved the issue for me: "follow the steps on this post apple.stackexchange.com/questions/284581/wipe-all-wifi-settings-from-macbook" (thanks, @axolotl)_