They do put some effort into getting you to create an account and go online in the installer.
And, when you boot the game, it instead boots a window GUI that I can imagine serves only to display the giant ad to upgrade to the more expensive version of the game. You have to search for the de-emphasized not-quite-a-button below to actually play the game.
This is one of the things I like about truly single-player games, where no interaction with other players is possible. Mostly puzzle games. None of those games have any of these dark patterns or unnecessary connectivity.
I have been enjoying Baldur's Gate 3. Offline :)