Erm... pushing data structures between APIs is the essence of countless viable businesses.

I love both FP and OOP and especially love using them together. I honestly don't get these arguments.

I think what frustrates me is that I see these people as, for lack of a better word, "posers". I'm no functional expert and I'm just in the beginning of my career, but I'm very skeptical of devs who had little problem with imperative/OOP code suddenly writing Medium articles saying OOP is dead and "functional" is the "next" step. Just makes me uncomfortable, but I'm learning to ignore it.

It wasn't an argument. I was asking a real question I am curious about.

Anything that behaves like an object, would be the obvious answer. GUI elements, things in games or simulations. More abstractly, an object's a namespace with persistent properties, so for something that has a persistent, possibly mutable, state, an object is the metaphor you want.

Whether data structures should be objects rather than primitives depends very much on the data.