This is termed the "broken window fallacy" in economics.

And sure increasing spending on military production creates jobs. But spending that money on improving infrastructure also creates jobs and you end up with a nice bridge you can use afterwards. Opportunity costs are a bitch, choices have to be made, and choosing military spending does equate to fewer resources for other things.

Don't get me wrong, I'm 100% in support of giving military aid to Ukraine. And ending the war sooner will have economic benefits by fixing the grain supply problems which is driving up food prices around the world. That's a good economic argument for it. "Broken window" fallacies aren't a good argument for it.

Also the general instability caused by this war leads to a lot of economic problems.

But yeah the main economic benefit it ending the war sooner. Ukraine is going to win this, it's just a matter of how long it will take. More support for Ukraine means the war ends sooner which less economic costs from the disruption in trade caused by the war.