I noticed that sitemap is usually created for a website. Is it also applicable to a mobile application?
As with many things "it depends". What's the purpose of a sitemap? what would be the purpose of a similar process for an app?
I'd argue that both are likely an artefact to model your information architecture, spot issues, like imbalance, orphans etc.
Both can be used to help inform a navigation system so can be equally valid.
A site map serves two main purposes.
1: The site is more navigable with a site map. A user can immediately get where they want to go without going through any intermediary pages. This can, of course, be better handled with good information architecture and good navigation design based on real user journeys and user feedback.
2: SEO. This is generally regarded as the main use for site maps on well-designed modern sites. The page is essentially a list of links to various parts of your product. Search engines see this as a way to understand your product and offer various parts of it in more refined results with greater relevance to the user. This is an opportunity for the product owners to display everything they have to offer and capture more of the market. For more information about fine-tuning a site map, you should look for SEO discussions.