You can also find tons of other examples of Apple's influence making decisions about what large numbers of people can experience, often without even realizing it is Apple pulling the strings, whether it be content about drugs, guns, or the use of sweat shops in the manufacturing of smart phones (a category of app I find particularly egregious for Apple to be censoring as it is so self-serving).
The core problem is really that there is no alternative: if your app isn't allowed to be accepted by Apple, you simply don't get to address something like half of Americans with your product. Users generally don't own multiple phones and they can't take an extra trip to "visit" another phone for your product, so attempts to draw analogies to supermarkets or Walmart tend to be unhelpful.
It is more akin to a physical region of the country... imagine more as if all Apple users happened to live West of the Mississippi River or whatever and you weren't allowed to sell there because they had a monopoly, and for users to use your product they have to take on massive switching costs (of moving across the country).
This centralized bottleneck on software development and distribution then plays out in tons of ways, and tends to make Apple a patsy for local government interference. People like to claim "they have to follow local laws!"... but they didn't have to build a product that puts them in so much centralized control in the first place, as except for in the most authoritarian of regimes (such as North Korea) pretty much everywhere is ok with relatively open devices (such as computers or phones that support sideloading).
Apple has thereby made an active choice to build a product that is bad for democracy around the world (including here in the west!) in no small part because it makes them a ton more money than one that they would have less centralized control over (and thereby manage to charge their extreme overheads on all use cases for)... this profits before people approach should be familiar, as it is also similar to the playbook used by Big Oil and Big Tobacco.
And, as we see in situations like this, maybe that Google merely allows sideloading isn't sufficient, given how they actively discourage it with functionality barriers (alternative stores not supporting automatic updates), discouraging messaging (telling users that side loading is dangerous), complex activation paths (sometimes requiring switches in hidden developer-only settings panels), and even stronghanding users back into their happy path (such as with their anti-virus-like tool that tends to flag alternative stores as if some kind virus).
We need to stop allowing this sort of behavior. If a company is doing something that puts them in a situation where they are making decisions to support authoritarian regimes, we should not only be morally judging them--and of course this includes everyone who works at these companies on these products: you don't get some moral pass for "merely" being a foot soldier if you have the skills to take on another job--but maybe putting in place laws that prevent our companies from tolerating these kinds of decisions.
And again: this is not to say that "you are asking Apple to violate the laws of Russia" or "you are requiring Apple to not sell to Russia"... the laws in Russia or China or wherever we tend to be talking about when these issues come up do not make it illegal to sell a device that lets users install this software: Apple, and in a different (though I do think lesser, if only for being more indirect) way Google, have gone out of their way to build a product that puts them in that position.
(To the extent to which anyone finds any of these thoughts interesting, I gave a talk at Mozilla Privacy Lab back four years ago on "That's How You Get a Dystopia", citing numerous examples of how centralized systems lead directly to the problem of gatekeepers either themselves becoming corrupt over time or being forced to corrupt themselves to satisfy external pressures, with numerous concrete examples--every slide is a citation--across the entire industry. The saddest part is that it feels like I am constantly writing down new examples of the issue I could use to make this long talk even longer, as this is a never-ending problem.)