The effect of doing this would be to unify Nato.
Russia has been trying to do the opposite. It was hoping for a red wave in the US elections (rumours are the withdrawal from Kherson was timed to be after this) and its hoping that cold weather will weaken government resolve around Europe as domestic pressure grow to force Ukraine into a resolution to the conflict.
Why attack a convoy in Poland when you can track it by satellite and do the same within Ukraine?
You also are crediting Russia with the ability to fly a missile or drone over the entirety of Ukraine (without getting shot down) and then hit a moving convoy with a fine degree of accuracy at this stage of the war.
Logic dictates you'd hit something static. But if you hit an airbase on Polish soil, believe me we'd already be getting one of those BBC breaking moments by now...
Russia, despite popular opinion, are not insane. Putin is rational. This hasn't slipped. And whilst he might be increasingly desperate there has to be a strategic advantage in hitting a convoy on Polish soil. Not a singular benefit of getting rid of one convoy. You need something a bit more worthwhile to take a gamble.
This does however provide a nice dead cat for those Russian pundits. And whilst they are talking about this, they are talking about Russians abandoning Olesky or Nova Kakhovka. Or Svatove mass surrenders or bullets in the back. Or stalemate at Bakhmut. Or the daily liberation of Pavlivka. But that's about it.
For all the talk. Putin's logic is warped and often misguided (thanks to his yes men and corrupt buddies) but he's also not stupid either.
Think logical here.
What does Putin actually gain by x move?
If Putin wants to provoke as response, you think a deliberate attack on a farm in buttfuck nowhere Poland is really the preferred target? "I know. We'll get the tractors. That'll show 'em how 'ard we are!"
FFS. Get a grip.