I admire your dogged idealism, and probably share your ideals to a large extent, but I'm afraid I take a far more pessimistic view.
I believe their is far more chance of a neofascist government made up of a unholy mix of Reform and the Tory Party taking power in 5 years time than any serious challenge forming from the social democratic left. Corbyn was as close as we're gonna get for the foreseeable, and we were screwed out of it by the nefarious worms currently running in the Labour Party in 2017, and blew it in 2019, a role in which Starmer played no small part due to his Brexit policy.
Sorry.