The most effective way to stop people having children in the modern world is to educate them and provide them with a middle class job. Any genetic trait that contributes to making it more likely for you to become educated or acquire a middle class job is going to become less frequent in the population now.

Another very effective way to stop people having children is to given them heavy retirement and old age medical care subsidies -- without having to depend on children for one's retirement / old age, one will have fewer children.

All that said, fertility rates among the middle class are not zero. They may be below replacement rate (ok, they are below replacement rate), but being non-zero means evolution still applies.

Also, obviously in the wider population (that is, world-wide) we might well be selecting against traits that lead to middle-class status (by having lower fertility rates in the middle-class), but still, within middle-class populations we're likely still selecting for those traits.

Yes evolution still applies.

Unless the middle class is a separate population to the rest of humanity then the evolution that is happening in the human population right now is selection against traits that lead to being middle class.

This selection is probably the strongest of any in human history looking at the demographic trends. When looked at dispassionately it is truely breath taking how huge this is.