I'm honestly fed up with these clowns - I've read dozens of comments like these, I was holding out on a 2015 Macbook Pro with High Sierra, because Catalina removed Widgets, but when the Widgets stopped working anyway I said to myself, why not upgrade to Big Sur? Big problem. Exactly the same issue - installation hangs many times, I restarted it. System then acts super-slow, got through the init phase, worked fine after that, except admin password does not work, so I can't access any preferences or my old files. Try restarting, system hangs at about 33%. Would have reverted to High Sierra which worked nearly flawlessly (except for backup to a NAS which was my major issue). Now reinstalling Big Sur just to see if it can go through - showing 6.5 hours to go just downloading. This is crazy stuff, hearing these stories from owners of even brand new Macbooks. Past High Sierra Apple starting screwing the system big time. I'm honestly beginning to hate this company.