The relevant close reason reads:
This question asks for recommendations for specific products, services, software, or electronic designs, which are off-topic as they attract opinionated rather than comprehensive answers. Please consider rephrasing your question in terms of what you should be looking for given your use case or whether a specific product has the capability you need.
If I follow by wording, yes, asking for a book (like here¹) is asking for a specific product. I'd assume that
does someone have a book aimed at me as a ham that explains electromagnetic waves for amateur radio enthusiasts?
is a product recommendation question, but
Can you recommend something I could read to learn about electromagnetic waves?
Is there some line that we draw?
¹ That question asks about recommendations for AM broadcast station operation, which is explicitly not amateur radio nor the technology of radio in general, but about practical aspects of operation of a professional mode; so it's off-topic anyway, imho.