The US exports military vehicles all over the world, and often is fighting against forces using them, in actual wars (as opposed to the Russia-Ukraine conflict, which is between Russia and Ukraine). We gave $18 billion in military equipment to the Taliban last year. That Ukraine has US military equipment means very little.

The US is providing security assistance to Ukraine, and condemns Russia's advance, but the US is not fighting a war in Ukraine

Almost every war everywhere is fighting with AK's somewhere in the mix, often on both sides. Arms is a very dirty industry and many governments play it, often with proxy dealers to allow them to be arms (da-dish) length and offer plausible deniability. Very often, a superpower or country ends up being shot at with the weapons it provided years or decades earlier.