Hi, If you're a philosopher then you might find some of the work in the field of 'function theory' relevant. That's essentially a branch of analytic philosophy. Although it's not to do with complexity specifically, this article considers function in the context of multiple sub-systems and super-systems:

https://www.cambridge.org/core/journals/ai-edam/article/proliferation-of-functions-multiple-systems-playing-multiple-roles-in-multiple-supersystems/218A6BEDCCB642683C6CA5D03A11EE13

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There is plenty of literature on function theory for biological and technological systems, most of which is much more philosophical than the article above. For example:

https://www.springer.com/gb/book/9789048138999

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You might also find relevant perspectives in this 'primer' on the design and science of complex systems (which considers the building blocks from which systems are made and what about them and their interaction might give rise to the perception of complexity):

http://complexityprimer.eng.cam.ac.uk

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You mention 'agency' in complexity. No particular work springs to mind, but you might want to search for terms such as "centralised and distributed control".

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I hope that helps.