The whole "let's replace Joe Biden with an invisible pink unicorn at the convention" thing is nothing but a fantasy that is apparently entertaining to some political and media types, but it is a delusion.
The time to get Biden not to run for reelection was late 2021. Which would have also destroyed his ability to get big progressive wins like the Inflation Reduction Act.
The politics of replacing Biden at this juncture are disastrous and no one should pretend otherwise: https://www.playtyperguy.com/p/ezra-kleins-plan-for-replacing-joe