Plan on playing Diablo 2 Resurrected offline? You'll still have to log in from time to time for authentication.
Like the original game, Diablo 2 Resurrected supports full offline play. Rightly so considering the Switch practically demands it. The game will still require you to go online and log into Battle.net at different points so Blizzard can make sure you own the game. In essence, D2R has offline DRM and the game can't be played completely online in perpetuity.
"An internet connection is required to download the client. Single Player mode may be played offline, but a connection to the internet will be required on occasion for periodic updates and authentication checks," the game's launch page says.
As frustrating as this sounds, it does confirm Vicarious Visions and Blizzard will continually update Diablo 2 Resurrected on consoles and PC. The devs teased that they have lots of ideas on new runewords, balances, and other additions that could come with future expansions.