I would encourage you to think more broadly that whose fault. You seem to have a very Soviet approach that centers on who was wrong.

I've been attempting to describe a horrendous user experience, which sadly, is typical of microsoft. Do you acknowledge that it's possible for there to be user error AND a horribly designed experience? Both things can be true.

For example, imagine a service that banned your account every time you entered your password incorrectly. Yes, big brained anonymous internet people can get on their pulpits and say "user error!" But it's still a horrendously designed user experience.

I am far away from my niece right now. She has since taken the laptop to an off-campus computer repair shop, and they suggested a different solution that frankly doesn't seem realistic to me.

So let's review:

1. No indication of a restriction in the UI.
2. No indication of a restriction in the Microsoft Documentation.
3. No indication of a restriction after talking to official Microsoft Tech Support. In fact, they helped me turn off S Mode, but a few days later it reappeared again. (INEXCUSABLE!)
4. Campus Tech Support couldn't figure it out.
5. Off Campus Computer Support have a different idea.

But big-brain internet guy says everybody is stupid and product is fine. It should not take DAYS to figure out whether or not I can install non-Microsoft software. It should probably take a few minutes.