The best we can hope for is either (A) Biden choosing to step down and let Harris run in his stead, and/or (B) Trump continuing to alienate the antivaxxers to the point where they refuse to vote for him, possibly combined with a split vote between him and whatever antivaxxer steps up to be the Republicans' next great white hope.
But considering Biden was dumb/egotistical enough to run in 2020 in the first place when the playing field was already full of better candidates, A is a pipe dream. And Trump, for all his ego, has already all but disappeared from the spotlight, with no sign of planning to run again. Hell, the dude started his reelection campaign the day he was inaugurated; if he had any plans to run in 2024, the official shirts and bumper stickers would have been printed up already.