Imagine a lot of gold coined into a foil and sent into orbit around Venus. Or even better, around the Sun in close proximity to Venus. On the inner side, so that the shadow and the darkness would fall on Venus. A silver or aluminum shield would do as well.
Now the nuclear winter on Venus begins. Snow made of dry ice would start to fall on its surface. Venusian atmosphere consists nearly exclusively of carbon dioxide; just as dry ice does.
How deep would those snowflakes fall anyway, before evaporation?
Not very deep at the present situation, since the local atmosphere is very hot. It has to cool down and the surface also has to cool down, before the two kilometers deep dry snow cover can form around the planet.
The problem is, that those rocks are heated from bellow by Venusian vulcanism.
So, you should wait for a very long time, before those rocks freeze very deeply. Until then, the climate on the Venus’ surface would remain very hot.
Do you still want to call this “a greenhouse effect”? Or would you rather call it “high temperatures caused by magma deep down”?