Why is your threshold 90%?

One reasonable way it could happen is that gradually AI and robotics starts to replace everyone in generally the easier jobs to learn.

So working in mines, as assembly workers in factories, as vehicle drivers, as warehouse pickers..these jobs will go first.

There are still plenty of jobs but they all require education/talent/physical characteristics. There's plenty of doctors - though they use AI to help them they still oversee it - and therapists. There are more SWEs than ever but you have to pass a test of talent to get the job. There are obviously many sex workers and webcam models but you have to be young and hot.

It's totally reasonable that it might be 10-50% of the population who are not employable for a period of time, until AI get substantially better.