Well it can't because how can they check if you're licensed to play the game? Connect to the internet first, then it'll let you start the game.

You wouldn't be able to.

GTA VI is not being released on the Xbox One. Game discs aren't DVDs and haven't been for well over a decade, they use Bluray discs, which won't even matter since GTA VI isn't shipping with a physical disc, only a code.

You need internet to access this product. You need updated system firmware.

An offline console would have no access to patches for any game (including the mandatory day one patch that kills off enough remaining bugs to make a modern game playable), downloadable content, or the all-important multiplayer.

Ironically, Xbox One support for true offline play was gutted when Xbox gutted a lot of planned Family Sharing support when Sony claimed the Xbox One was not going to allow you to play games offline and made that a marketing campaign with pawn shops like GameStop. (The same campaign that also called in-box Kinect a mistake and complained that the Xbox One was too "media focused" and "not for real game players".)

The resulting early Xbox One pivot removed features that would have been useful when systems were down and replaced them with "offline capable theater" instead. (The same pivot that also killed the Kinect and Xbox One multitasking and host of other useful media features.)