I have a late 2012 iMac, and am currently running Mac OS10.15.7 (Catalina), which I installed almost a year after launching! I understand, however, that I will not be able to upgrade to Big Sur (MacOS 11). I read this morning about iMac specs for OS11 being late 2014 or later.
I am planning a new iMac in the future, but first want to await the development of the hardware (ARM processors). I used to be an early adapter, but no longer since I retired.
Completely right… High Sierra is the latest OS my Pro 2011 is compatible with. PL 3 still works on that one - at times rather slow when working in large file.
My newly purchased 2020 has Catalina installed from factory. PL 3 works fine, but if I would decide to run Big Sur, would it still do so… Since DxO now had a nice price on update to PL 4 , I took offer. But Big Sur will have to wait. I’m not too keen on bugs.