I am from the future. Joe Biden wins in 2024 by more than in 2020. What happened?

[Mister Mets]

This would be a relatively normal development.

Richard Nixon, Ronald Reagan, Bill Clinton and George W Bush all won reelection by bigger margins than their initial election. Biden's win was narrow, so there's room for improvement.

There are many potential explanations.
1. Events- An economic recovery in 2024 is possible and would be great for Biden.
2. Candidate Trump screws up- Former President Trump could easily run a terrible campaign, or there could be some other major error (IE- a bad Vice Presidential pick from someone who had to be talked out of Christie and Gingrich.)
3. Trump sabotages the Republican nominee- If Trump doesn't seek the nomination again, or if he loses a primary, and feels insulted by the Republican nominee, he's certainly capable of saying and doing stuff that will hurt the party.
4. Major third party campaign- If there's a divisive Republican primary, a MAGA independent ticket or establishment independent ticket could split votes, and help Biden's margin.
5. Demographics after all- The country is getting less white, but it hasn't helped Democrats as much as expected. But maybe 2024 is when it all happens. A variation of this would be if a reliance on evangelical voters (which may be more about how conservative Christians identify themselves than the way this was understood pre-Trump) scares away centrists, or boosts left-wing turnout.
6. Democrats learn discipline- Given the extremes of the parties, any party that goes with the center with strong message discipline may be able to win in a landslide. I don't think Democrats will be able to thread the needle of keeping the base happy while focusing on popular issues, but it's possible.
7. Major Republican scandal- "Grab them by the pussy" didn't end the Trump campaign, but it's always possible for something big to happen. Maybe a 78 year old Trump is caught on video saying something stupid, or Ron DeSantis proves not to be teflon if he has a Rielle Hunter or Bridgegate style problem in October 2024.