I'll keep it short and simple: one thing that I was discussing with my fiance, about the hostilities in Ukraine, is that, apparently, Western nations are refraining from sending more modern weapons to help Kiev's regime precisely because they're aware the Russians would capture them and, soon enough, there'd be both counter-measures for those plus suspiciously similar designs appearing in Russia and, mayhaps, China.
Or would that be too difficult to happen? What are your thoughts?
I think there is a simpler explanation: Ukraine primarily gets the stuff that is easiest replaced. The eastern European countries started by delivering their old-but-still-working Soviet Arsenal and replaced it with more modern western stuff that they got from Germany.
Also I think Russia and China have a pretty good idea what the bulk of western weapons and munitions are like. There might be some super specialized or highly advanced stuff that might be news to them, but that wouldn't be given to Ukraine anyways ($$$).
And as long as the West doesn't deliver trained engineers and a fully equipped factories to Ukraine the risk of high grade weapons technology being stolen seems low.