There are a few instant-death instances in Baldur's Gate 3. If players make a certain decision with the Dying Mind Flayer, it's immediate death. Also, shooting certain objects while aboard the Nautiloid results in an explosion that can easily kill the team in a single blast.
Baldur's Gate 3: How To Disable The Guardian Statues
Getting killed in one shot happens often in Baldur's Gate 3 and the Guardian Statues have some of the highest kill counts in the game.