I recently updated to macOS Big Sur 11.0.1 and I faced the same challenge. The network data transfer rate dropped over Wifi. These are the following steps advised by Apple Support: A. Reconfigure the DNS steps: System Preferences Network WiFi Advanced DNS tab Add 8.8.8.8 or 8.8.4.4 Click OK then Apply B. Adjust Packet Size steps: System Preferences WiFi Advanced Hardware tab Configure location from automatic to manually MTU 1453 Save/Apply C. Change location and renew DHCP lease steps: System Preferences Network WiFi Edit location Add location Advanced TCP/IP Renew DHCP lease Click OK then Apply D. reset NVRAM and SMC. attached are the articles for the steps do the these resets. Reset NVRAM or PRAM on your Mac - https://support.apple.com/kb/HT204063 How to reset the SMC of your Mac - https://support.apple.com/kb/HT201295 (To know your machine has T2 Security Chip: OPTION-KEY+CLICK ON APPLE LOGO >> System information >> Controller)

I recently updated to macOS Big Sur 11.0.1 and I faced the same challenge. The network data transfer rate dropped over Wifi. These are the following steps advised by Apple Support: A. Reconfigure the DNS steps: System Preferences Network WiFi Advanced DNS tab Add 8.8.8.8 or 8.8.4.4 Click OK then Apply B. Adjust Packet Size steps: System Preferences WiFi Advanced Hardware tab Configure location from automatic to manually MTU 1453 Save/Apply C. Change location and renew DHCP lease steps: System Preferences Network WiFi Edit location Add location Advanced TCP/IP Renew DHCP lease Click OK then Apply D. reset NVRAM and SMC. attached are the articles for the steps do the these resets. Reset NVRAM or PRAM on your Mac - https://support.apple.com/kb/HT204063 How to reset the SMC of your Mac - https://support.apple.com/kb/HT201295 (To know your machine has T2 Security Chip: OPTION-KEY+CLICK ON APPLE LOGO >> System information >> Controller)