I see this rhetoric a lot and I really dislike it and find it actively harmful to people with ADHD.

ADHD, at least mine, would absolutely still be a mental illness outside of modern society. My doesn't care if I'm remembering where I put down my phone or where I put down my sandwich, I still misplace them either way. At work being without my medication makes it difficult to keep track of my responsibilities. At home it makes it difficult to keep track of doing laundry, washing dishes, cleaning the house. You don't suddenly lose all responsibilities and idle tasks without a modern society, your responsibilities and tasks just become different. And my ADHD couldn't give two shits what those responsibilities and idle tasks are, I'm going to struggle with them either way without medication.

Dismissing ADHD as not a mental illness but a symptom of modern society is not only incorrect at it's most basic level, it also implies that people like me could be "normal" IF "x, y, or z" conditions were met. That idea is just blatantly untrue and just perpetuates the dismissive and uncompromising stance that many people take towards individuals with ADHD.