The most obvious possibility is AOC. In that case I am sure she'll move even further right and get totally ratfucked by the party regardless. That's the most jokerified option, I think. At the very least, her obvious ratfucking will push many more people to the left like the Bernie campaigns did.
But the worst possibility is some rando Democratic apparatchik we've never heard of like Mayo Pete showing up. They take up all the aesthetics of Bernie's campaigns, they receive the glowing endorsements of Bernie and the squad, but they seemingly refuse to outright promise anything we would call "good", and they suspiciously receive no material push-back whatsoever from the Democratic party establishment other than some clearly bad faith grumblings about how spooky and radical this person is. Win or lose, they completely suck the energy out of leftist movements in the imperial core for a further decade.
Jeff Merkley is my sleeper prediction. He has some similar beats to 2016 Bernie: no one knows about him, is left of the majority of dems, has a relatively safe seat in Oregon, history of regularly voting against the majority of the senate for things like military budgets, is a socdem. He tried to run in 2020 but wasn't able to convince the Oregon state government to allow him to run for senate and president at the same time.
Though I have my doubts that he has the energy or charisma to rally up the support. Otherwise, I see Pritzker as fitting the role.