I am looking for freelance jobs that would allow me to work remotely and part-time. From what I see, apart from coding jobs (most of which seem to be full-time), only jobs as scientific editor come up. Does anybody have any experience of freelancing as a Physicist/Mathematician with academic background? What would be your suggestions in terms of websites, job titles to look out for, etc.?
A third area, in addition to @MichaelLai's first two, might be financial services. But, alas, that would also be lots (and lots) of programming. However, you'd also be developing models requiring lots of math.
I have an ms in physics, but most of my work has been programming models for the financial services industry in New York City. For instance, binomial tree models (e.g., https://en.wikipedia.org/wiki/Binomial_options_pricing_model) to solve the Black-Scholes equation (e.g., https://www.hoadley.net/options/bs.htm) Take a look at those pages, and I think you'll agree that your math background will be put to pretty good use (albeit lots different from C*-algebras, etc:).
Also, my experience is mostly contract programming in New York City, where financial services comprise a large segment of the city's economy. I know nothing about San Diego. And also, although contract programming is typically hourly, I've usually been expected to put in hours that amount to full-time work, or even more hours. However, on various occasions I've had fixed-price contracts, where you agree to deliver a product/project for an agreed-upon fixed price regardless of the hours spent. Then your hours are up to you, although the contract usually has a calendar time-frame for various deliverables leading up to the finished project. And that can be a daunting constraint, depending on how well your experience has prepared you to develop the model.
I think that two of the areas that you can definitely look into would be in the area of AI/machine learning for something more specific, or you can brand yourself as a data scientist if you just want to do general data modelling and analysis of 'big data'.
Most people that I know who are well-trained in the mathematical sciences seem to be picking up work in this area.