So, I upgraded from Catalina and my MacBook Pro 16 and it is a secondary device. I didn't notice too many bugs at first until I started using third-party apps. I noticed that in the Security section of Preferences I had like 10 "system extensions" being blocked. I checked them all and clicked Allow, but when the computer rebooted they were blocked again. The only way I solved it was to reinstall one of the applications, reboot, and click allow on all again. That seemed to get everything unstuck. As for the Spotlight launching the wrong apps and thumbnails being incorrect, I haven't had those issues.