Although the macOS BigSur update is a landmark for UI change and expanded processor compatibility, large changes can herald equally-large compatibility problems. Some WiFi users find that their connections drop or experience other issues immediately after installing this update. In such cases, there are many solutions that users can try instead of rolling back or reversing something as critical as an operating system update.
These recommended solutions assume that you already have fully updated all related software and aren't using out-of-date drivers. Outdated software packages can result in various performance problems and always should receive updates as soon as possible. Users also should reboot before jumping to conclusions about their hardware and avoid using hibernation or sleep mode as an alternative to a real system restart.
Resetting any WiFi router may correct connection problems. Unplug the router from power for thirty seconds and plug it back in. The router's manufacturer may provide more detailed recommendations on resetting a router – even to 'factory condition,' if necessary.
WiFi users also should note the Personal Hotspot feature. Creating a Personal Hotspot can help with testing whether it's a specific network channel or a device that's not functioning. It also is worth testing whether or not any other USB devices conflict with the WiFi; unplug them as necessary.
Creating a new WiFi Host Configuration also may help resolve network connectivity problems. In any macOS environment, open the Finder app, and disable the Wifi connection. Create a backup folder with any memorable name. Then, use the 'Go to Folder' feature to go to the '/Library/Preferences/SystemConfiguration/' location. Move 'com.apple.airport.preferences.plist,' ' com.apple.wifi.message-tracer.plist,' 'NetworkInterfaces.plist,' and 'preferences.plist' to the backup folder. Reboot the computer and set WiFi to 'on.' If this solution doesn't work, restore the files to their original location.
Another step that's useful for WiFi dysfunction is creating a new location for the network. Go to System Preferences and then to the Network section. WiFi should be visible on the left side of the window. Select it, and click 'Edit Locations' from the Location field. Name the new location anything memorable and click 'Done.' Then, select 'Advanced' on the bottom right. On the TCP/IP tab, apply 'renew DHCP lease.' On the DNS tab, click the plus button for adding new server addresses. Add the addresses '18.104.22.168' and '22.214.171.124.' Finally, on the Hardware tab in the same window, choose a custom MTU and '1492' for the value. Apply this change, too, and click OK when you finish.
Some sources recommend resetting the SMC or NVRAM settings as part of correcting macOS WiFi problems. These hardware settings handle low-level functions such as temperature management and disk selection during startup. Experts don't recommend that casual users modify them without supervision. However, users may resort to them if all other solutions fail at correcting the WiFi issue.