I find systems design and complex adaptive systems fascinating. I really recommend the book, "Hidden Order: How Adaptation Builds Complexity" by John H Holland. It is technical but aimed at the educated, non-technical reader, with enough description that you could code along to his models. I really wish he had written more books. RIP.
Another good source of systems thinking are the books by Jane Jacobs on urban planning.
I think anyone wanting to study this area rigorously would need to spend time doing detailed discrete event simulations, understand probability theory, time series analysis, phase space analysis, experimental design, graph theory and queueing theory.
Like databases or operating systems, complex systems embody many fields of study simultaneously. One of the funnest parts is that they can be modeled at so many different levels.
Complex Adaptive Systems https://en.wikipedia.org/wiki/John_Henry_Holland
Urban Design https://en.wikipedia.org/wiki/Jane_Jacobs
Ants https://theconversation.com/e-o-wilsons-lifelong-passion-for...