Trump is totally going to run in 2024 unless he dies.
I could see Biden not wanting to run. But then who could beat Trump? Kamala is too black and female. Fox News is doing their hardest to Hillaryize her and it's probably working in a number of key states that Democrats need to win (I'm thinking especially in the rust belt). Mayor Pete is too gay. That's still a major disqualifier for a large segment of the population (including major constituencies of the Democratic party). You know that it'll be really easy for large segments of the electorate to fall for the cheap homophobic attacks that'll be leveled on him. "Pete is gonna legalize trannies in sports! He's going to groom kids! Look at how weak and decadent we are, Chasten is the first lady hahaha!" And if you don't think those attacks won't have a significant impact on the electorate, then I truly wonder if you know anything about America.
Democrats have plenty of moderates, like Klobuchar ann Whitmer, but they'll be destroyed for being women. Remember, we're just a few years away from "Trump that Bitch" being a thing. Again, if you don't think Whitmer won't attract a ton of sexist attacks, then you must not know America at all. A bunch of other Democrats are either too hispanic (go back to Mexico Rep Castro), black (Corey Booker wants to urbanize your neighborhood!), female (Trump that bitch), or urban to win in the general.
It's really tough to win the EC while trying to maintain a large tent. It's much easier to just juice your base with homophobic and bigoted attacks and reap the rewards of the reactionary structure of the EC that benefits ruralists who are falling increasingly behind the rest of the country economically and culturally... Meanwhile, Democrats need to excite turnout in urban areas while also winning the whiter and more conservative rust belt areas in order to win the EC. That's why Biden was so attractive. If you go with someone younger, black/brown, gay, or female, you'll probably lose the rust belt and hand Trump a 2nd term.