I'd assume they are talking to him about doing reshoots and looping for the Snyder Cut. But I don't know how that works. For the theatrical cut that would all be in his contract for the movie--so they wouldn't have to pay him extra and he'd be committed. But for the Snyder Cut, I would guess that they do have to pay him extra.
So maybe if they're talking to him about that, there's something else they've put on the table. I gather he didn't agree to do the cameo in SHAZAM! because that would count as the last movie he was contracted to play--and then they wouldn't have to offer him anything else. He was holding out for more than a cameo, I think. So another cameo doesn't seem in his best interest unless it leads to more.
If there was one movie, other than a Superman solo, that he ought to be in, it should be a Supergirl movie. That's the one property where the lack of Superman would irk me the most.