One of the primary quests of Baldur's Gate 3 Act One is "Find a Cure." The protagonist and the first set of party members all have a mind flayer tadpole in their brains, and they'd much rather get them out.
Baldur's Gate 3: Find a Cure Walkthrough
Players will end up searching a lot of corners of Act One to find a way to get rid of the mind flayer tadpole.