After two hours on the phone with some excellent Apple Care+ advisors, my iMac is back to being a modern computer. I was trying to avoid an erase-and-install of Big Sur — which got me in this mess to begin with — but in the end, it resolved the problem. Back in business with a snappy computer.
I’ve always been a huge fan of Michael McDonald and the Doobie Brothers. On Apple Music today I found this interview with McDonald. Great stuff about his work with Steely Dan.