I think Daniel Bryan's gonna be the catalyst for the Punk heel turn.

Bryan comes back, he's a white hot super babyface, he and Punk have a segment together and they end up tagging in a match against - let's say 2.0 because they've been targeting big names. They play off the fact that Bryan and Punk tagged together in Punk's final match in ROH. They have the match against 2.0; Bryan starts off the match and it's fairly well balanced but Bryan's doing well, eventually though 2.0 start wearing him down, stopping him from tagging Punk, y'know how a tag team match goes down you can picture it. Punks got his arm out for the hot tag as Bryan rushes to the other side of the ring in desperation - but he tags the air, Punk brings his arm back at the last second and looks down at Bryan.

Bryan still manages to win, but barely, and as he's laying on the ring exhausted Punk comes back into the ring and beats the shit out of him and he's got venom in his eyes. Punk comes out at the next show and explains everything, he's like "let me tell you a story" and it's all a thinly veiled allusion to how when Punk left WWE, that was a catalyst for Bryan ending up in the main event of WM30. He can talk about how when he was in pain, while he was suffering during one of the lowest points of his life he saw Bryan at the top and he heard "Yes" chants everywhere he went because he put Bryan there. It became a symbol of everything that made Punk sick, everything that kept him away from the thing that he loved for so many years. After coming back and hearing about Bryan coming in to AEW, he was willing to forgive and forget, but he couldn't because Bryan never "thanked me" - and that becomes a whole thing during their feud, that Punk just wants to be thanked for making Bryan a big star.