Here's what they should do IMO. It's not the answer that will please the Internet, but at this point, I think it'd probably be the most effective method for getting things back on track for the DCEU barring a complete shutdown and total reboot. Reshoot the ending, with Barry having been changed into a new actor too due to the change in the multiverse. Allude to Superman being around somewhere, but by no means do you tie it to the Henry Cavill version. Heck, Sasha Calle's Supergirl can even be wearing a different costume for added effect that the changes in this timeline extend out past Earth and into other planets like Krypton. Don't bring Batfleck back in that post-credits scene. Don't even think about keeping that teaser in. No teasing for some sort of Crisis on Infinite Earths or something big that gets "ALL THE GANG BACK TOGETHER OMG." Clearly a sizable chunk of the remnants from the old guard messed with an ancient eldritch evil or something, because one thing or another keeps coming back to act as an albatross for the franchise. Just carry over Jason Momoa, Gal Gadot, Margot Robbie and Viola Davis from the Snyder era of the DCEU and move on with the post-2018 guard. They've all easily been the most successful elements of that era and have already been able to move on with the DCEU post-Snyder to great success. So with that, start fresh. Have Keaton's Batman continue acting as a Nick Fury type across the new DCEU, introduce Nightwing, let Gunn make a Harley & Ivy movie, find the right team to make a Green Lantern film, get Joseph Krosinski to reboot with an already established Superman for the new continuity and keep pushing on.