There are a few layers to this problem. They're not entirely wrong about developments in AI-assisted coding – it is progressing quickly. But for now, LLMs doing "any software engineer job" is still far off. At least in the way people like your brother mean it: that some non-technical person can just tell an AI "build <this or that> for me," and the AI handles it end-to-end.

Until we reach that stage (if ever), technical people will still be needed in the loop – to check that the AI's work is correct, integrates properly with the rest of the system, and meets the requirements. And this leads to the main role of any engineer: figuring out the requirements. In other words, determining what exactly needs to be built.

People, in general, aren’t great at describing things in a precise, unambiguous way – and non-technical people even less so. I don't see this part of the equation being automated anytime soon.

As long as you enjoy figuring things out, solving technical problems, architecting software systems, and understanding software at a deep level, I think there will be work for you for the foreseeable future – no matter how "AI-assisted" it becomes.