I guess it depends on what kind of step-aunt you mean. I've seen in a lot of porn situations a step-aunt/uncle is set up to be an new spouse of an uncle/aunt, when they'd be the cousins' step-mom/dad. I've never heard of that type of relationship be referred to as step-aunt irl. They're already related only by marriage, so them being a second, third, etc spouse normally would have no bearing on what your relationship to them is. However, relatives of a step-mom/dad are referred to as step-[relation] in some families. Usually, any family that bothers to distinguish between a parent and step-parent will carry that distinction through to the rest of the step-parent's family. I think, though, that step-[relative] distinctions mostly serve the same function as [relative]-in-law references, in the sense that even in families that do use them they're primarily used as a shorthand to refer to those complex relationships when speaking to outsiders about family matters rather than used to speak to them in person, which you'd normally just use their name for. Even in the situations I've heard it used though, it requires knowing the person and their family situation to make sense to use it. Like, if you're meeting someone's step-aunt but don't know that they have a step-parent or which parent is the step-parent, then being introduced to a step-aunt is just going to be confusing, so even when applicable the usage is pretty niche
