I have this problem too, maybe Screen Time Restricts access to the Internet here it is Check for Any Software Updates & Restart Your Mac. ...  Disconnect All USB Devices from the Mac. ...  Create A New Wi-Fi Configuration in macOS Big Sur. ...  Create A New Network Location With Custom Settings. ...  Reset the NVRAM on your Mac. ...  Reset the SMC of your Mac. ...  Reset the Wi-Fi Router / Modem. Try to connect to a different network.

Try running Safe Mode on your Mac by holding shift after restarting the Mac, you will temporarily access to the internet. SAFE MODE CONTAINS LAGS

I had similar issues on macOS 11.0.1, but Zoom still works!

There is 11.1 released, hope it fixes this issue

Does Big Sur 11.2.3 fix these issues right now?