DO NOT confuse a better than expected Democratic showing at the midterms as some kind of mandate for Biden. He is a terrible President, and the Democrats need to do better than him in 2024. I believe he will be defeated if he runs, but the Democrats, if they are smart, will choose a better candidate to run.
Biden is just barely ok to me, but whatevs. He's "terrible" but getting some important shit done (infrastructure, lowering prescription drug prices) when the courts aren't nixing initiatives (student loan debt relief, which I fully support even though I paid mine off 4 years ago). But you're right that the results aren't a mandate. Per the exit polls, there were many people that weren't personally enamored with Biden's performance that voted for Democrats anyway. Biden won more of those voters that disapproved of him than Trump did in 2018.
If Biden runs in 2024, his reelection depends on who wins the Republican nomination. DeSantis = Trump + discipline + adult attention span thus he's a more formidable opponent.
But Biden is far less likely to lose to Trump if Trump gets the nod. As for Biden's inherent advantages, he's pretty much a middle-of-the-road guy. That's what allowed him to win the 2020 nomination in the first place. Also, as someone on Fox actually said last week that unlike Obama, people don't really hate Biden that much. It's hard to dog whistle that the president is black (oh the horror!) or a woman when he's an old white guy that's prone to being corny.
Trump is also advantageous against Biden because in addition to not accomplishing much, Trump is so polarizing and utterly abysmal in every conceivable way that he motivates a significant portion of the electorate to always show up to vote. He fluked into one win because of the Electoral College (and an unfocused opponent who was equally loathed in Hillary) and that's been it. No other president has lost the House, Senate and presidency in one term like Trump did. Even well before DeSantis' strong win last week there were focus groups that concluded it was wiser to move on from Trump not because GOP voters no longer love him but because he's a constant drag on the ability to win (because this GOP, counter to what Senator Patrick Moynihan called the GOP in 1981, is the party of winning and not the party of ideas). So despite the current right wing media pitting Trump as the fall guy for the midterm results and suggesting DeSantis is the future, the source of the entire problem plaguing the country--the GOP voter--has yet to have their say.
. I think I'm slowly being converted into the whole Dark Brandon meme after all. 
