OMG. I wrote yesterday here about the site techsviewer.com and the use of the App "cleanmymac". However it solved the problem only for one day. Now the MacOS Big Sur is very very slow again. The CPU consume is sometimes high and sometimes low. The process "WindowsServer" consumes sometimes 50% of trhe CPU. WindowStats also. It is impossible to make my work (Software Development and hear Youtube music) like this. If this s*** continues I will install Catalina OS and skip Big Sur forever.

My MacOS was very slow too after upgrading from Catalina to BigSur. However, I followed the instructions on the site below and the problem was eliminated. techsviewer.com/macos-big-sur-slow-fixes-here You have to install the App "cleanmymac" in order to follow the instructions above and uninstall some old apps and services that are consuming your CPU and memory. Best Regards, Jocafi