Biden, assuming no blatant, derailing health conditions is going to run again & will face no serious challengers from the Democrats. The ones who might are in his Cabinet & won't oppose him. He's not going to "step down". It would be suicide for the Democrats if he did, IMO. Basically a pre-admission of defeat & almost conceding the next election to whomever the R's put up. They couldn't run on Biden's record, which has actually been quite impressive, even if not enough. And I don't see anyone else, outside of maybe Newsom, who would even register on the general public's radar.
To clarify what I'm saying: there are absolutely better Dem candidates out there. But not ones who could realistically win against Trump/DeSantis/[other R who wins their nomination]. And the voters are much more likely to care about that than supporting the current version of Ralph Nader, or Jill Stein, or making a "protest vote". I say this because I believe that lesson has been learned the hard way, too many times, across too many age ranges & voter blocs. Just pointing to the Supreme Court & Trump's THREE appointees is enough to illustrate that point, I think.
What happens if "this candidate isn't good enough!!" happens again like it did in '16 & Trump 2.0 or DeSantis gets control from '25-'28? Losing the Supreme Court for not just the next 20 years but for the foreseeable future? Not to even mention the issues the left, most left-leaning moderates (also honestly a lot of right-leaning moderates I know), & the younger crowd care about: LGBTQ rights, Climate Change, income inequality, college affordability, election integrity, etc. - they would all be dead in the water instead of advancing slower than they'd like.
Basically: Vote Electable>Ideal. Don't Let the Prefect [sic] Be The Enemy Of the Good. I think that lesson has been hammered home? At least, I hope it has.