Big Sur total lock-up like so many others on this thread. Apple progress bar stuck at 30%. Tried booting into safe mode, internet reset and then 2 hrs last night with Apple technician chat. Another hour this morning. No joy; I now have an appointment at the local Apple "Genius Bar". What Apple genius a)released software that does this and b) hasn't fixed it in over a year? At the very least this should come with a health warning for older machines (mine is a 2015 Air)