I would pick AI, because it's a growth industry with on-going innovation. You would also be able to work in many different kinds of applications. It seems like it would be fulfilling work.
You didn't mention why you're uncomfortable with trading. Finance used to be a great choice, but it's not a growth industry now, innovation stopped after the Financial Crisis in 2008, and the industry has been saturated with PhDs for over a decade. Meaning math PhDs not in demand very much anymore in finance and most of the work is not very interesting anyway.
Personally, I wouldn't pick crypto ("blockchain") as a lifetime career.
Note that any of these career would require significant effort and learning on your part. You didn't mention what your PhD in mathematics is in. You would be competing with PhDs who have done their thesis in something highly relevant to AI or finance and/or have done a great deal of research on the topic before applying for jobs in their target field.
If you don't care about how much money you'll make, and enjoyed your PhD work, then I suppose postdoc would make sense. If you don't care about money and didn't like the academic environment, then you could go into teaching relatively easily with your qualifications. Perhaps teaching / lecturing at a private school or college, if not a university. I would suggest that you do care about money though, because it is an important factor in determining your quality of life.