Slow user switching
Fast-user switching has become slow (15s freeze) since I moved to Catalina.
I frequently switch between 2 user accounts. Switching under Mojave was reasonably fast. But under Catalina, the machine freezes literally for about 15 seconds. With either the color wheel spinning, or the spinning gear freezing (if the login screen is displayed).
I have a mid-2018 MacBook Pro 13" with 4 cores, so the age of the computer should not be the issue.
MacBook Pro with Touch Bar