I am still on Catalina and trying to upgrade to Big Sur and Software Update says that it is not available. What do I do?
I cannot update to Big Sur. Software Update says that it is not available.
iMac Line (2012 and Later)
What model year is your iMac?
The model year of an iMac is available at Apple menu > About This Mac.
A late-2012 through late-2013 iMac can be upgraded to Catalina 10.15.7 but not to Big Sur.
A mid-2014 or later can be upgraded to the current version of Big Sur. See: https://support.apple.com/en-us/HT201475