The existing law outlines the complicated process. Biden cannot do it instantly. Here’s an overview of the process that’s already been done so far

Now the rule has been proposed so we’re at the end of that graph. That’s what I mean when I say we’re close. Here’s the actual rule making procedure to do the rescheduling

https://www.federalregister.gov/documents/2024/08/29/2024-19370/schedules-of-controlled-substances-rescheduling-of-marijuana

Additionally, it’s worth noting that earlier, dem senate leader was also perusing a legislative path until it was clear they couldn’t get the votes. Hence later executive action