You don’t need to log in or be online to play. I don’t understand the purpose of Larian’s launcher, but it is not distruptive.
Larian launcher is used for telemetry. Every time the game cashes, it spawns a window for you to explain the crash and send the report. It also allows to select either DX11 or Vulkan, although Steam allows to do that natively so it is a bit redundant. Also it allows for Larian to show you their merch.
