I am wondering what jobs in the field of Mathematics are (seemingly) always in demand. I am also wondering what jobs there are that are (once again seemingly) greatly Mathematically demanding in regards to either deep specialisation or great generality in the application fields.
For the second criteria, I mean that a great amount of learning must be done to understand the career. Whether that be learning a lot of content from multiple fields, or significant investment in a specialization.
More specifically, what fields meet both of these criteria?
Thank you for your time.
Note: If you wish, give it in regards to any location you wish, I understand this can be (and likely is) location reliant.