Hi @irahandler Thank you for your question!
In this case, the difference lies in the nuance and context of "algún" and "cualquier", even though both can translate to "any" in English.
"Algún" (shortened form of "alguno") implies a specific but undefined option from a group or category. In this example, "¿Tiene algún libro de aventuras?" asks whether the person has at least one adventure book in mind.
"Cualquier", on the other hand, means any at all, without specificity and is often used when expressing that any option is acceptable. However, it doesn't fit in this context because the question isn't about any book, but rather if the person has some adventure book available.
To summarize, use "algún" when referring to an unspecified but defined option, and use "cualquier" when the choice is open-ended or indifferent.
I hope this helps clarify the difference! Feel free to reach out if you have more questions.