I don't see it either. The hard left wing would make an exception for Bernie because who else do they have, but they won't give Biden a second look. For most it won't be a change from what they already have with Trump.
I just talked to two millenials that recently bought a house. They secured a 3% loan, they both have good jobs, and have money to travel. I know several in that position so I really don't think Biden is a practical change for them. Socialism is an idea that doesn't carry over well in the US economic structure. It sounds good on paper but the reality is nobody wants to pay for it, especially anyone that has any money in the bank or invested. Mostly I see socialism entrenched in academia but that isn't the real world. Very few people can actually live there.
Probably vote 3rd party protest or stay home and T locks down another one.