No, Steam Deck does not require an internet connection. You can use it offline as well.
SteamOS is designed to be an operating system for gamers, and the Steam client is used to manage games. As such, they will need to handle updates and downloads for games accordingly.
Fortunately, Steam Deck will also be able to function offline. This means that gamers will still be able to play their favorite games even if they’re not connected to the internet. After a game is installed, players can play it while the Deck is offline. This will allow gamers to enjoy their games without worrying about whether or not they’re connected to the internet.
But, many games require an internet connection. They are often multiplayer or DRM games. There is always DRM for single-player games like Just Cause series and the Hitman series to name just a few. This means that if your internet connection goes down, you can’t play the game offline. Gamers have mixed feelings about this policy. Some argue that it’s a necessary evil, as it helps to prevent piracy. Others argue that it’s an unnecessary nuisance that only serves to inconvenience paying customers.
In conclusion, a Steam Deck only needs to be online when its user has to browse the store for downloading new games or to play online multiplayer games, or bypass a game’s DRM.