Earlier quoted context omitted.
Apple has a monopoly on selling phone apps to the percentage of smartphone users that have an iPhone in their pocket. It should thus be regarded as a monopoly regardless of how many people are affected, and forbidden.
If we accept this definition of a monopoly, then the term becomes worthless. Every single device where the user can add third party software but it has to be approved by the manufacturer becomes a monopoly. Stuff like Garmin watches, "smart" fridges and other appliances, "apps" on car's dashboards (like Spotify on Tesla etc). And why should this only apply to hardware, is it not comparable to Facebook having a monopo…
I don't see the downside of requiring everyone in your examples that already allows third party apps to do so for free (other than passing through payment processing fees) and without delay and censorship: the costs are minor or insignificant and can be included in the purchase price of the device.
The advantage is that it leads to a fair playing field for app makers, lower prices for consumers (since the money that goes to the platform maker is all visible upfront in the device price and thus easier to compete on) and doesn't stifle niches that the platform owner doesn't like for whatever reason.