First, the hypothesis we use commonly says that natural selection occurs when there is competition amongst the population so if we as a population are competing for these medical advancements then semantically no, evolution is not necessarily stopped because a population gets technology. There are a few faucets to evolution but Darwin's null hypothesis says that if there's competition then there can still be evolution occurring.

Logicaly arguing, at first, any change we make to the environment would be to benefit us more in the short term. Think antibiotics for example. At first we cured lots of diseases but in the future we will have made more deadly ones. The more changes we make to the environment the more it will change and assuming we evolved to do well in that environment, the changes we make might seem good immediately but will have unforeseeable effects which may be more detrimental to us in the long-term. Then again, maybe they wont be because that depends on all the other decisions living creatures are seemingly making in spite or simply jest of the laws of physics.

Still, humans are nature and we are just a small part at that(no matter how much our egos tell us we are the biggest, our egos make us human, they do not part us from nature). A huge catastrophe will cause a special evolutionary event I think termed "bottlenecking" or I don't know the academic terms if you look type in: "bottlenecking, catastrophe and evolution" you should get some textbook material that comes up to explain how that effects the population specifically.