I tried to install Big Sur on my 2014 iMac yesterday. Now my computer is completely frozen - it won’t install the new system, and it won’t let me go back to the old one. My computer was working fine before this, and Apple has been of no help whatsoever. I have a deadline for work and I am losing it. I have tried multiple reboots, etc. Screen stuck on “17 minutes remaining” since last night. That’s where it always gets stuck
