You are assuming the government was going to spend 6 billion on food and medicine before any of this started. They weren't. If the authorization to sell the oil was never given there would be no money to argue over. Once the oil was sold it was legally Iranian money, not ours. We had this issue earlier with Iran if you remember the $8 billion we had to return. So if you are going to blame Biden you have to also blame Trump for issuing the waivers in the first place.
https://www.nbcnews.com/news/world/...e-selling-oil-its-8-biggest-customers-n931891
Lastly if anyone thinks Iran used the "fungible money" since the announcement of the release to purchase, take possession of and deliver to Hamas in the Gaza Strip they are crazy. The planning, aquisition and placement of the military equipment had to have taken months to implement. The Iranian assistance could not have gotten there in that amount of time. So unless you think Iran and Hamas knew months ago that the money was coming, the "fungible" part of the debate doesn't work.