Yeah. In practice with Windows the machines would all get the same update but Windows Update might say it’s availalable for each machine at a different time, depending on the roll out schedule. I think most of the experimentation happens on machines where the user opts into the Windows Insider program. But I haven’t paid close attention to Windows updates in years so take Windows specific details with a huge grain of salt.

In general though, for some random software they might release an A version witha ad at the top of the screen and a B version with the ad at the bottom and then use telemetry to figure out which version is the most effective.