Even though Darkseid won’t be at the forefront in Justice League, since he appears to be the DCEU’s overarching evildoer, there’s a strong chance he’ll end up being the main villain in Justice League 2 (which currently doesn’t have a release date).
Eventually DC’s main superhero team will have to face off against him like their comic book counterparts have on many occasions; the question is when.
The giant Omega symbol burned into the ground and the Parademons flying around confirmed that Superman had help from Apokolips, although only hardcore comic book fans understood the full implications of that vision.
Darkseid’s existence in the DC Extended Universe was revealed in Batman v Superman: Dawn of Justice when Bruce Wayne had a Knightmare where he was a resistance fighter on an Earth taken over by a rogue Superman in the future.