The symptoms is always generally poor performance after the system has been running a while (4h to a week, varies), usually with WindowServer using CPU cycles non-stop and UI that felt choppy across all programs.
This seemed to happen frequently after "opening many files", like doing some recompiling with Xcode for a few hours, or indexing a large volume with Spotlight. Rebooting helps temporarily.
Today I realized that data read/written since boot was about 1TB in a few hours on a brand new OS install, and I traced this back to the com.apple.Safari.History process. Somehow having bookmarks and previously using Safari 15.x caused a huge amount of I/O that wouldn't stop - the solution was to remove all bookmarks and reading list items. Performance was immediately back to normal, no reboot needed.
So just logging in with your iCloud id, you could be "importing" whatever performance problem you're having on a new install.
I recommend you reboot and take a look at your disk I/O stats - maybe this will help someone!