He walked that back almost immediately after getting into power.

Advisor in Campaign (Dec 2019): “If Biden is elected,” a prominent adviser to the campaign said, “he’s going to be 82 years old in four years and he won’t be running for reelection.”. This was solely to get people to vote for Biden before Obama saved his campaign on Super Tuesday.

January 20, 2021: "He's planning to run again," Chris Coons tells politico. This was literally the day of his inaugeration.

March 25, 2021: Biden: "I'm running for reelection in 2024."

Nov 22, 2021: Biden intends to run for reelection in 2024, Psaki says

It was only ever a ploy to get people to vote for an old ass piece of shit.