This forum contains lots of insights and I would especially like to hear from people who have a PhD and have gone back to school. I received my PhD 22 years ago and my job prospects are so abysmal that I have thought about going to law school or pharmacy school or whatever will actually lead to a real job with a real salary. Has anyone taken the route of retraining after the PhD? Was the expense of yet more schooling worthwhile? I have heard, for example, that law is no longer an attractive option because there are too many unemplpyed and underemployed lawyers, at least in the USA. Is this true of other fields?

It's great that you are considering going back to university after such a long spell in industry.
More people should do this because the number of 40-50 year olds who feel trapped is ridiculous. I didn't do it after a PhD but I did return almost 20 years after graduating with my first degree.
I understand that you want to earn at the end of the degree but in my opinion this is a really poor reason for putting yourself through half a decade of stress and it may not work out that you get the job you want anyway.
I would advise you to go back if the main purpose in doing so is a driving desire to do that particular degree. If that is your main driver, everything else will follow. If you only want the job you might find that the difficult times during the degree become impossible. You don't want to end up hating what you are doing. Also, your degree journey might lead you to avenues you haven't yet thought of.