I mean, I don’t like the interconnecting of the MCU as a general rule, it has been criticised as something which is bad for consumers (and bad for storytelling). In their case it’s inherited from comic books…which is also bad, and has been criticised. Endless crossovers requiring you to buy issues from other runs that you might not be interested in? It sucks! It’s a major thing people complain about for Marvel/DC comics.
Direct sequels aren’t the same thing though, since they’re…direct sequels.
Neither of the above are exactly FOMO though because they’re not time limited; it’s not like if you don’t watch Infinity War in cinemas then they delete it forever, or maybe promise to re-release it at some unspecified time (for a brief window) in 2-5 years. They’re still there, and the comics* are still there.
*…to some extent, obviously getting physical copies is more difficult than that, but in the digital age it’s a little simpler.
FOMO is most commonly seen in live service games. Like WoW, like Overwatch, like Fortnite and Destiny. Any content which exists and then is no longer available is a form of it, though arguably moreso when you know it’s going away.
Zul’Gurub OG getting deleted by Cataclysm wasn’t really FOMO (at its release, at least) because people didn’t think it was going away. Ditto for the legendary quest in MoP.
But event skins in Overwatch, rotating trading post items, battlepass exclusive items, and even arena elite sets are, and they’ve all long been criticised for it.
People were generally accepting of the trading post’s FOMO mechanics beforehand (though it had received criticism) because there was no real money attached to it. It was viewed as a bonus for a subscription (something that a lot of people had asked for).
But once you start tying it to real money purchases? Not so much, because now you’re manipulating people to drop more cash on it, which - for the reasons I’ve gone over above in this thread - can impact game design.