It is just crazy. Made a clean install of Big Sur 11.1 and it worked "ok" I would say. Had a startup on my iMac 2017 of about 5-6 minutes. Way worse then Catalina but ok. Now automatic updates that I do not have cancelled put 11.2 over it, and again 15min startup. Nice one apple really nice one. AND the biggest let down is that time machine backups from Big Sur are not compatible with Catalina. So Catalina setup requires completley manually copying of all files really nice apple.... I am done with Mac OS next one will be windows again...

Same issue here on iMac 2017 1TB Fusion Drive. I really regret this update so hard, I already waited some weeks and thought now everything should be fine. But as you all reported really long times to boot. Afterwards it works ok I would say but the booting unacceptable slow with up to 10minutes