Pretty much the only thing it spoils in the trailer is probably the one thing you already know.
I can't tell if this is supposed to be some time after the end of IW, like they've been saying it would be, or if it's just, at most, a few months after. It doesn't feel like years have gone by. Everyone seems to still be in a state of shock.
I'm pretty sure Tony is going to be rescued by Captain Marvel. She's the most logical choice to swing by and pick him up from space. Then something with the quantum realm is going to be central to their plan to save everyone, which also includes time travel. I don't think they should but pretty sure Cap is a goner, except they are gonna try and give him some happy ending with Peggy, which I am calling shenanigans on right now if that is the case.
You would think, but no. The only way for Steve to get some sort of happy ending and getting the life he lost out on with Peggy, he'd have to go back in time... and if he does that but doesn't go and save Bucky, then it makes him an asshole. And we know already that they are planning a Falcon/Winter Soldier buddy superheroes series which means that Bucky has to still fall, still be found by the Russians and brainwashed and endure 70 years of torture and horribleness in order for that series to happen. So. Steve can't get his happy ending without sacrificing his best friend to his horrible fate and that does not seem like a Steve Rogers thing to do. The only acceptable alternative is he swaps himself with Gamora into the soul stone and Peggy is there waiting for him. But that feels a little bit creepy to me, like the reality is they're now trapped in there rather than getting some kind of eternal happiness. (But I guess it would be a way for Marvel to bring back either character should they choose so... hmm.)