Finding a place in interdisciplinary sciences as someone who develops computational methods and algorithms for other fields?
There is a concept of a research programmer, but it's pretty rare. My primary degrees are in maths and social sciences. While my PhD is in computer science, I use programming as a tool to do social science and am not really a great programmer. However, there is a lot of programming in the research projects that I tend to be involved in. For some projects, we would include a research programmer - someone with excellent programming skills who is doing methods development research. That is, the person would be developing new algorithms to solve some social science problem and implementing it. It sounds like this is what you are trying to find.

If so, such jobs do exist. However, they do not lead to a stable academic job since there's not a clear set of subjects that such a person can teach. Furthermore, the jobs are fairly rare.

Nevertheless, if you want this sort of job, you really need to work out what you ARE interested in. That is, economics or physics or whatever else. After that, you can think about what sort of problems are amenable to computational methods for their solutions. For example, look at computational social sciences (I do network science and agent-based modelling) and computational economics.