Am well aware war is stupidly expensive, but I really can't shake the feeling someone or somemany are skimming quite a bit of these helps and donations. Every now and then we see huge amounts of money given to Ukraine, to a level that is approaching GDP of some countries, and yet there's never enough of anything.
You can't shoot money as artillery munition, first off you'd need a driver load and then it'll get all messed up. There's not enough shells because the west doesn't have much production capacity and doesn't deliver much, it's as simple as that.
The stuff the US sends is overwhelmingly surplus hardware, kind of hard to make disappear, especially the large stuff. Reporting a rifle as lost to the enemy even though you grabbed it for yourself? Quite easy, but won't work often before people get suspicious. A whole crate? Command will have your ass. Stealing an Abrams? Forget it.
It's the EU who is sending the most of the money and practically bankrolling the Ukrainian state -- their economy isn't exactly in a good place right now, tax revenue is low, and all the tax revenue they have they spend on the war. Thus, the EU is picking up bills for wages of civil servants, pensions, such stuff, to avoid Ukraine having to pay people in flour, onions, sunflower oil and eggs confiscated from farmers. Not good for morale, that kind of war economy.
As to corruption in that area: EPPO has a working agreement with their Ukrainian counterpart, and seem to be very content with it. EPPO is the EU's prosecutor office, investigating and prosecuting crimes against the EU budget, headed by the gal who cleaned up Romania.
Ukraine no doubt has an issue with corruption -- but also a people long fed up with the consequences of it, a government fed up with it, and a war that noone wants to see lost because of it, and a national identity that would like to very much distance itself from terminally corrupt Russia.