Leaks, like live-service games and always-online requirements in single player titles, are one of those realities of the video game industry that we've just got to live with.
Leaks are a bit different from the other two though, in the sense that they've been around much longer, and are usually perpetuated by the community, not the companies (except when bug leak things first). They also very often get debunked, but not often at warp speed like this latest GTA 6 rumor.
Grand Theft Auto 6 is one of those nebulous projects were we know it's under development but it hasn't been announced and isn't being talked about by the developers or the publisher despite having passively osmosed more hype than some of the most heavily marketed AAA games. It's been said that Rockstar Games could tweet the image of a palm tree and break the internet harder than celebrity posteriors.
With the main rumor on the block being that the next title in the franchise is taking us back to the pseudo-Miami of Vice City, every minor detail that can be made to fit this narrative is being latched onto both by fans and by rumor mills looking for clicks. This is what happened just recently, when a leaker erroneously drummed up a 2002 domain registration as the confirmation fans have been waiting for.
Big game companies often don't just secure the specific domains they choose to host their sites on, but a broad array of other domain names that are similar or close, as well as various misspellings and then get all of these to redirect to the actual site. This is done to idiot-proof the system and also prevent "domain jockeys" from snatching a similar domain and either profiting off it or extorting the company. Look no further than the famous lawsuit between Microsoft and MikeRoweSoft.
When one particular GTA 6 'news account' was looking through the domains registered by Rockstar Games, they encountered rockstarcartel.com and jumped to the assumption that this is related to GTA 6 and Vice City. Miami was always known as a hotbed of drug trafficking, a theme extensively explored in the original GTA Vice City.
While things seem to line up, there's just one hitch in the theory - the domain was registered way back in 2002, the year the original Vice City game was released. This is blatantly displayed on the domain information screenshot posted initially, and handily pointed out in the comments as well. What may have thrown the curveball was the fact that apparently the domain was 'updated' on April 12, 2021, but seeing as navigating the link now redirects users to the current Rockstar website, it's possible that was the change.
This redirect updates the url to include a "domain-check-failed" error that usually denotes unauthorized access to a page, but before you think there is a secret GTA 6 website we're just not allowed to see, this same error is seen when navigating to any number of domains that Rockstar Games has registered but does not use, such as "gta6.com". This too does not mean that there is an actual GTA 6 website, it's just the company preventing from you or me or anyone swiping the domain with the intent of selling it back to them at an exorbitant sum.
Nonetheless, Vice City still remains everyone's best bet as far as the setting of the next GTA game, which we know for a fact is coming. Though it would be uncharacteristic, there is a chance Rockstar might rear their head at E3 this year, but we'll have to wait and see.