My colleague "took one for the team" by updating to big sur. Only the corporate VPN access that broke so no biggie.
My iMac is a late 2013 model (even though I bought it Mid-2014).
The issue I have is that it wouldn't connect to the internet, even though it was connected via Ethernet cable.
After 5 hours on the phone to Apple Support, they have concluded that there is nowt wrong with my IMac and the problem is my Network.
I promptly moaned at the building manageress (very lovely she is too) and they put me in another office where my IMac worked perfectly.
The tested my connection and found it worked flawlessly with a laptop connected. I plugged my IMac back in, and it didn't work.
So am now using WiFi.
God knows what the answer is. But at least I can work.