Actually it’s more like being upset that Facebook friends show up in WhatsApp.
The user in the link is upset because their IG profile is now visible in a different service and they did not explicitly consent to this.
And of course there is such a thing as a Threads account, you even refer to it in your second paragraph. Just because they share a common IDP doesn’t mean they aren’t a distinct service. It’s effectively single sign on without the appropriate privacy protections.
It’s cool that you’re into the whole thing, but other people aren’t and they have a right to be pissed off. GDPR and the like weren’t created for no reason.
I forgot about the anti cheat stuff. That may well be an issue - some VM toe-dipping appears to be in order for me