One could argue they also are free to decide to buy some property that makes that so hard to be effectively impossible.

People do that all the time with game consoles, cars, fridges, smart light bulbs, etc.

So, does anything differentiate smartphones from those? If not, arguing all of those should be opened up, I guess, wouldn’t make it through the justice system (¿yet?)

If it’s “if the seller allows installing some apps, they have to open up for all apps”, game consoles would be affected, too, and one could argue that the likes of Fortnite would be, too (that isn’t hardware, but neither is iOS, and it’s iOS that people want to install apps on. If Apple opened the iPhone, but not iOS, I doubt people would be happy)

If it isn’t that, what is it that differentiates smart phones?