All - my 2012 iMac running Yosemite 10.10.5 system software cannot be upgraded to run AC23. Does anyone know if there is a hardware part (CPU maybe) that can be changed out so latest Apple OS can be installed?
"Bob" - Church of the Sub-Genius
Graphisoft afficionado since 1993
If it is really a 2012 iMac (vs an older one purchased then), it can be upgraded to Mojave (and should have been a long time ago). Mojave will run AC 23 just fine.
Since you have not updated at all since 10.10 (5 version of the operating system have been released since then)... it may be a fear of updating? Be assured, when you upgrade your MacOS, it has not affect on your data files and settings - only the OS. Still, it is wise to do a complete backup before updating!