Congress controls the purse, they have been providing foreign aid to Israel since long before he was elected. Biden directs the armed forces, and is using them to supply aid to Gaza.
That said, the US has been ‘helping both sides’ for ages. We provide more money to Israel than any other country, and also contribute more to UNRWA than any other nation. The goal of the US has been to reach a two state solution, so it makes sense to fund both states.