I upgraded to Big Sur today but not without a glitch. I successfully downloaded the upgrade via Software Update but when I ran it, I got a window with no progress bar but nevertheless had an estimate of time remaining to prepare the hard drive. Eventually, it had a message that it was quitting open apps and waiting to restart; this never happened. The computer then went to sleep according to my Energy Saver preferences. I woke the computer, quit Installer, and restarted. Then I ran Installer again, and this time, all went well except that the initial Big Sur screen was faded, and I had to click in the window to make it appear normal. (Naturally, I had updated two clones of Catalina beforehand.)
I will have to get used to the new appearance of Mail and Safari which, initially, I don't like. My wife will issue lots of complaints so I'm bracing for her wrath. My printer software had, for no apparent reason, reverted to Airprint, which I do not want. Consequently, I reset the printing system and reinstalled the Epson driver. I had to redo my presets, but that wasn't a big deal.