I just got my MBP 2020 Quad yesterday. fresh install of all my apps and I was getting Beach Balls in almost every app in the System Preference window took 8-14 sec. to open. If I clicked on Users it would take 14 sec. for the Icon to open up. On any System Pref. if I clicked on the Security Lock on the lower left corner... Spinning Beach Balls.
Well I worked with Apple Support all day, I was ready to return this thing after my third re-install.
I know this is long-winded but I put in a lot of time on this new 2K laptop. So what was the fix for me... Change The "User Image" under Users & Groups. Yep and then Bip, Bam, Boom as soon as I changed that old self portrait which was imported under my Apple ID. Everything Worked. Just a suggestion.