Just a note - Used OCLP to upgrade my mid 2012 Mac Pro to Big Sur. While it took a bit of time and a couple of manual re-boots all went fairly seamlessly. However the 'upgrade' changed all of the permissions with attached HD's - internal and external. So took a bit of time to reset. For some unknown reason I lost the last 3 weeks worth of Time Machine BU's. OTOH I did get a 'graphic' asking if I wanted a 'tour' of my NEW MAC PRO. That had me smiling for the rest of the day.