From Comicbook.com:
Marvel’s Eternals is beginning to ramp up its marketing and promotional campaign, following the film’s big Hollywood premiere. Obviously, as the first wave of critics and fans get to see Eternals (and learn its game-changing secrets for the Marvel Cinematic Universe ), there are certain details of the film that will cause a big buzz. Marvel Studios has apparently chosen to give one of those secrets away for free, early, by releasing a new preview for Eternals that reveals that the characters of the MCU are all too aware of the existence of DC’s god-like hero: Superman.
