Hope this link will help: https://www.cnbc.com/2017/06/28/20-jobs-that-pay-over-100000-with-the-least-competition.html
It details high-paying jobs that don't have much competition in the field. Good luck!
How smart of you to start your research by trying to understand where there is demand in the job market. Makes perfect sense to me! In addition to that fantastic link you have been provided in the previous answer to your question, you are right to keep in mind a basic economics principle (I know your question isn't really about economics but just bear with me for a second :))....a basic economic principle of supply and demand...when demand is high and supply is low, there is an opportunity of get more value for or from that thing..in this case, "get paid a lot" for working in a specific field. I will share that I have been in the working world for quite a few years and, as an engineer and programmer, I have never experienced a time when there wasn't a need for an engineer or a programmer, even though I don't know that I would suggest that these fields are underpopulated. I would suggest instead, that the demand is out there. Technology and/or STEM-based fields will always, in my view, have demand from employers...
So the next SUPER important thing....what type of job, work environment, company, supervisor, do you want to work for? Most reputable companies understand that if all they have to offer is a high salary, the likelihood that they can hold on to good employees is lower than if they can offer other benefits, in addition to good salaries. Things like a safe working environment, opportunities to learn new skills, opportunities to work or volunteer within a specific community...these become some of the things that reputable employers add on to encourage candidates to apply (and stay) with their companies.
Hope you find this answer helpful and best of luck to you!