Most recent Mac OS compatibile with CS 5.5

[lb_fred]

Hello. I am running CS 5.5 on Mac OS 10.8.5 on a late 2009 IMac 21.5 inch. I would like to upgrade to a more recent OS that will still run CS 5.5. Any thoughts?

[John Waller]

>> late 2009 IMac 

I suspect the latest operating system you can run on that is macOS 10.13 High Sierra which will definitely run CS5.5.

macOS Mojave (after High Sierra) requires iMac (Late 2012 or newer)

https://support.apple.com/kb/SP777?locale=en_AU

See what Apple says

https://support.apple.com/en-us/HT208969

Note: Catalina is the very latest version of Apple's operating system but a) it will definitely not run CS5.5 (or any 32 bit software), and b) your computer won't be able to run it anyway. So forget about Catalina. For your computer, it's either High Sierra or Mojave.