

Sci-fi is delightfully circumspect on how an intergalactic empire would work. Maybe Herbert’s Dune universe is clearest and he just took us back to the middle ages with sandworms and drugs, fiefdoms and nobility.
I think whatever area shares the same government is a country. It doesn’t have to be contiguous or on the same body floating through space. It could be the size of the Vatican or half the universe.
I suspect the definition of the word will change once (if) we make it to the stars. We have gone from nomadic life to loosely defined borders to kingdoms to empires to multinational and intranational federations of sort. These terms may no longer be fit for purpose when we colonize Mars etc. And maybe that’s why you struggle to comprehend how it would all work behind the scenes. We don’t know for sure, sci-fi authors don’t know (or don’t want to be too specific and limit themselves in what stories they could tell in the future).
I think with PCs it will be harder to lock them down and not disgruntle consumers too much in the process. I’m also hopeful that over time right to repair will be the standard, so they have to allow for third party repair. So all these restrictions like chipped components and software only from our store will be phased out by incremental legislation. The EU is not perfect but it’s on this path. Even in the US people are thinking antitrust more often now. There is hope, however small.
You can run whatever you like in your Android phones. Jailbreaking iPhones is also possible. All these devices are just computers that can run anything within their hardware specs. Hacking some of these things may be against the Ts and Cs or even illegal. But technically possible. The restrictions are mote political, not technical.
Chromebooks are not the way to the future. They fill a niche in education for cheap hardware in connection with limited capabilities. They are not technical limitations, they are designed to limit users in what damage they can do. AFAIK you could technically wipe a chromebook and put Linux on it. It may violate the Ts and Cs and we’re right back at political. Google would like to develop future customers at an early age. They don’t care about the education so much as about their bottom line.