I, Joseph R. Biden Jr., do hereby grant a full, complete, and unconditional pardon to all current United States citizens and lawful permanent residents who, on or before the date of this proclamation, committed or were convicted of the offense of simple possession of marijuana, attempted simple possession of marijuana, or use of marijuana, regardless of whether they have been charged with or prosecuted for these offenses on or before the date of this proclamation
The FDA has nothing to do with drug scheduling. That’s the HHS, DEA, and AG. Congress could just take marijuana off the list if they wanted, but that’s not likely to happen any time soon.
OK, one of those three letter agencies, regardless my point stands - the president can’t do it.
He can, though. He can issue an executive order to the DoJ telling them to stop prosecuting people for non-violent weed offenses.
That does not legalize it.
Those are all part of the executive branch, and are subject to the executive.