It would be very strange if American weapons weren't used in a conflict this big, which is a very different question from "did the US government sell weapons into this war".
I've looked for articles and don't see anything about US weapons. It would be very strange, indeed, but supposition isn't proof and I can't find anything suggesting the US is involved in anyway. Colour me surprised, tbh.
I wasn't here to 'provide proof'. Just pointing out that any conflict beyond a certain size almost certainly has some weapon from every large arms producer deployed in the field. I can't image how many tons of small arms we left laying around in Iraq, Afghanistan and the rest that are now being recirculated around the worlds conflict zones. I remember after the Soviets pulled out of Afghanistan if you were in the right place and knew the right people you could get cases of NIB AKs for like $25 a rifle (no, I didn't). It's not politics...it's logistics.
Guess you are on the wrong side of things if you know your weapons are getting laundered through other countries to get to a conflict. And of course uk, us and china know this and always knew this.