I created the account just to respond to this thread. Last weekend, I was basically forced to "upgrade" to the BS (Big Sur) system cuz I needed to download iMovies but it no longer supports my "old" OS that came with the MBP I purchased in 2019. Like so many others, the progress bar got stuck at ~95% when rebooting. I tried everything mentioned here, but nothing worked. I was only able to reboot in "safe mode" and get into the "fancy" "Big Sur (BS)" system, but could not do anything other than browsing the most basic web pages. I wasn't able to open any documents or log into my online drive, and most importantly, external hard drives could not be recognized! After wasting over 7 hours of my life trying to sorting out the mess, I called the support and talked with a technician over the phone for another 2 hours. I could tell that he tried everything, but still at no avail. He then presented me with two options: 1) wait for more experienced "Apple engineers" to investigate (which could take a very, very long time), or 2) erase everything and do a "clean install" (which still would NOT guarantee that it would work). What a Sophie's choice. I went with option 2), and asked for an extra day just to email my most important documents by getting into "safe mode" again. This is not the first time I got screwed by Apple. Last year, I lost all the photos and text messages on my iPhone after "upgrading" the system. I suppose Apple has given me enough reasons not to trust their products so much again, and I'm now more open than ever to trying out new brands

Over a year later, still the same issue. Apple is really going downhill, fast