The reality is nobody knows where all the money goes. Its an intentional financial labyrinth; a maze that beneath a smokescreen. That is no conspiracy theory.
I get the sense that you either don’t understand how it works, or you intentionally want to ignore how it works.
Arms transfers are done by virtually giving the receiving country a “store credit” and a list of the arms that are available. In the case of Ukraine, all of these available items are coming from existing stockpiles.
Nothing is being “bought” and aside from munitions, very little is being produced. The money has already been spent and the arms are generally a generation or two older than our existing arms.
Now, we can disagree with how and why those arms are being sent to Ukraine. But no cash is exchanged—at least not to the tune of “6 Billion dollars”. And $6 Billion dollars worth of arms being sold on the black market would be pretty easy to detect.