Q: Cannot spoof MAC Address on Macbook Pro 2019 13.3 on Big Sur Beta 4
I had same issue, your solution actually works
sudo ifconfig en0 ether yourspoofedmacaddress

What you have to do is hit up arrow in terminal and keep reentering it rapidly about 3 times and then it changes.  I needed to do this to Login to a captive wifi and my IOT devices can't do that so have to spoof from my Mac.