CS5 is a 32-bit/64-bit hybrid. Modern macOS (Catalina and later) will not run CS5 because they have dropped all 32-bit support. You will need a virtual machine (like Parallels or VirtualBox) running an older OS like High Sierra.
Introduced advanced painting capabilities, allowing you to mix colors on the canvas and define "wetness" for more natural strokes.
CS5 was the first version to offer native 64-bit support on both Windows and Mac. The "White Rabbit" Easter Egg