Of course Iran wouldn't block its own ships at its own checkpoints, but the US is capable of easily interdicting Iranian shipping if it wants to.
If that is agreed upon it's going to come with some concessions by Iran which is even less likely.
USA could agree to it because it's not particularly dependent on that fuel supply and therefore would only pay the costs indirectly via market forces, which as the thief-in-chief pointed out, does (the parts he cares about of) their economy no harm as a net petroleum-product exporter, and above all else, they are losing the war.