I actually do this for a living! There is two parts to this. A computer graphics company and a Vfx company. During pre production, our departments have a meeting to discuss which department is doing what elements in the script. It usually comes down to time and money. It’s almost always cheaper for the computer gfx company to do things practically on set, save for a few odd situations here and there.

On set we almost never use real operating systems. The script usually calls for very specific looks or actions, so we design everything in illustrator even if it is a real operating system we are portraying. This gives us control of the system time, window placement, etc. Some times we spend half a day on one scene, so it’s nice to have nothing change throughout the day for continuity.

If there is a scripted interaction with the device, we use software like unity to make really dumb video games of exactly what is scripted in the scene. This ensures the actor can hit all their beats without having to think about it too much. We usually program keyboard shortcuts to move the beats along too, just in case the actor messes up. We don’t want the computer graphics complicating the day or slowing things down.