Ask HN: Recommended resources on learning about search?

While looking for a potential new role, I noticed that there were a few job openings specifically for a search engineer (not a generic backend engineer role). These aren’t roles for building a search engine like Google but are instead working on the search system of an app. I haven’t worked on search outside of rolling out small solutions using Elastic or a cloud provider’s search service.

Are there any good blog posts, whitepapers, or books that you’d recommend for better understanding the problem space?