(edited)
I have noticed that after I got installed KB5003637 (which is presented as a 21H1 fix) I have the same issue. Computer is not only slow, but it is not a CPU usage issue. More like a lock or blockage of some event queue.
I have seen...
Complete block after adding new tab in edge or chrome.
Icons very slow to load on facebook.com and scrolling down also halts again and again.
maps.google.com freeze on zoom-out using touch pad.
Writing this message actually without any halts at all.