The two biggest influences on this election IMO were

1. Andy Burnham being blocked from standing for election by Keir Starmer, because Keir was scared that Andy could challenge his leadership of Labour. Pretty much anyone you talk to in Gorton / Denton agrees that if Andy had been standing he would have won.
2. Tactical voting against Reform UK. It turns out that fascist ultranationalism is quite unpopular with some people, who will vote tactically in order to keep them out. Labour and Green were both polling pretty much neck and neck, but the tactical voting websites went with Green, for two major reasons - among voters most likely to vote, Green had a small majority, and also because Labour voters were much more willing to tactically vote for Green, than Green voters would be willing to tactically vote Labour. The Gaza Genocide has made Labour completely unelectable among a good chunk of the voter base.