The only thing that atrophy when not coding is coding.
I think maybe we're conflating strictly cognitive facilities, facilities that can be maintained through all sorts of means, with intellectual skills and habits that really are in danger of atrophy when we rely too much on AI.
The AI age is trying to automate away our thinking, which runs the risk of making our brains look and feel like the same way as our bodies if we don't actively try to use them.
In the case of exercise, the majority of people don't pursue it in a somewhat post-labour era. I'm certain we'll see even less mental exercise in a post-thinking era. And it's deeply unsettling to think about how that will play out if we don't wake up and put a bit more mandatory thinking into the way we live with AI.
Anyway, I'm still writing the vast majority of code by hand and only getting AI to check my work at the end as an extra reviewer. I still am happily employed and sure am a lot happier with my job than the slop goobers posting here.
I still do LeetCode problems occasionally. It feels weird to write code and work through complex logic manually again, but I think it's more crucial than ever these days. It's like physical exercise. If you don't use your brain and keep challenging yourself, your problem-solving skills will eventually atrophy.