Like I can imagine him enthusiastically siding with protesters could have either turned all centrist off, or perhaps galvanized the population into rabid support. There'd be actual optimism in the air. There'd be a groundswell and a gameplan.
Or chuds might have felt extra threatened and started accelerationist, captial murder sprees.
Covid? RBG? Post office? West coast fires?
The protests may not have gone on as long/as disruptive if people believed there was someone who would lead and confront these issues, though Bernie's "cops need more money and training" response would have gone over like a lead balloon.
The party would not unite behind him, so it would be up to his supporters to recruit a bigger pool of supporters. I really do think the Democrats would rather lose with Biden than win with Bernie.
I don't know if chuds actually know the difference politically between Biden and Sanders, they smear Biden like a socialist anyway, not sure if they'd have to do anything differently for Bernie.
In conclusion, this country is too stupid and evil to ever get good things.