There is a certain amount of expected "lock-in" for social media and network effects, as you say.

I think there are classes of product that have an outsized amount of power and should be subject to more strict judgement on this however.

ISPs, payment processors, web browsers, general purpose operating systems, etc... all of these should not discriminate and give partners an unfair leg up.

Chrome should not block bing.com from loading, and should publish everything needed for anyone to write a webpage Chrome can render. Windows should not block iTunes from running, and should publish specs on how to write software for win32 APIs. iOS should publish airdrop specs to allow alternative implementations.

The rest of my complaints amount more to norms for certain things. It has become the norm that someone who sells digital books, music, or movies allows people to access them on the platforms they're on (spotify works on iOS and android, ditto for youtube music, etc etc). Apple is the only company I know of that abuses an OS+Media monopoly for basically all media, like Amazon has the Kindle, but they still let you read books on normal Android too. Apple is violating the norm in a way that feels intended to create an anti-competitive moat.

Similarly, every other messaging app is cross-platform, and iMessage not being cross platform, banning users who use it on android (https://news.ycombinator.com/item?id=39156308), and refusing to publish their own android app, that also feels like it violates the norms of messaging apps in a way that is either gross incompetence, or anti-competitive.

I think Fortnite doesn't qualify as an "operating system" because it can't gatekeep how someone interacts with competitors. If, in some weird future, Epic started selling "Fortnight Decks" (like the steam deck), included the "Deck Apps" app store, and it became a general way of computing for some appreciable fraction of kids, then yes, I think that hypothetical "Deck Apps" store and the device could have such lock-in and I'd have the same complaints.

I also think if fortnight became the default way the next generation communicates (akin to iMessage), it would indeed be wildly anti-competitive if they partnered with Google, and made it so the chat app was only available on ChromeOS.

However, as it is now, Fortnite isn't violating norms, nor is it going out of its way to gatekeep access to the community, nor is it anyone's gateway to general computing, so it doesn't feel comparable to iMessage, nor to the app store.

Also, what do you mean by "coy" there? I don't understand the meaning in that context.