THR is reporting that Henry Cavill will not be returning as DCEU's Superman. This is because of a number of factors as mentioned below.
That's because the studio has shifted its focus to a Supergirl movie, which will be an origin story featuring a teen superheroine. This effectively removes an actor of Cavill's age from the storyline's equation given that Superman, aka Kal-El, would be an infant, according to DC lore.
Furthermore, Warners isn't likely to make a solo Superman film for at least several years, according to another source. "Superman is like James Bond, and after a certain run you have to look at new actors," says a studio source.