Given that Kit Harington has been cast to play Dane Whitman, a human, this presumably means that some of The Eternals will be set in the present day, although if Harington’s Whitman will be/become the Black Knight, perhaps our visits to the past will also include seeing some of his ancestors rocking that mantle.
So far no official plot details for The Eternals have been revealed yet other than it will explore events that happened tens of thousands of years ago in the MCU and, just like their comic book counterparts, they will be protecting Earth from the malevolent Deviants.