What the offline label does and does not establish
Offline support concerns the listed game experience. It is not a promise that every bonus, account service, download or future feature works without a connection. The product's legal information allows internet or account requirements for certain features.
This guide describes the PS5 listing. It does not establish the contents of an unopened physical disc, a day-one update requirement, or identical account behaviour on Xbox. Check the edition and platform you actually intend to use.
Sources: [1]
Prepare the right PS5 for digital offline access
Sony's Console Sharing and Offline Play setting lets people using the enabled console access purchased, downloaded games while offline. An account can enable this setting on one PS5 at a time.
If you have more than one PS5, confirm which machine has it enabled before a trip or a planned internet outage. Changing that console can affect access for people using the previous one. This is an account setup check, not a GTA VI-specific workaround or a substitute for owning the game.
Sources: [2]
Keep ownership and memberships separate
PlayStation Plus provides services including online multiplayer for most games and cloud save storage. Those benefits are separate from the offline-play setting. A subscription name appearing elsewhere on the console does not by itself mean you must purchase it for GTA VI's listed offline experience.
GTA+ is another subscription, managed separately from PlayStation Plus. Before accepting a promotional month, check eligibility and the displayed renewal date. On PS5, open Account in Users and Accounts, then Payment and Subscriptions and Subscriptions. You can review the next payment or cancel a service there; cancellation takes effect at the next payment date.
Sources: [1][3][4]