Why is my page 'Discovered – currently not indexed' even though it's in my sitemap?

Being in the sitemap tells Google the URL exists; it doesn’t make Google crawl or index it. “Discovered – currently not indexed” means Google has found the URL but hasn’t crawled it yet, often because it rescheduled crawling to avoid putting too much load on the site. I’d use URL Inspection to check the canonical URL and make sure the page is reachable to Google, then give it a clear internal link from a relevant indexed page. If it’s only a few new URLs, give it time. If it affects lots of pages, look for slow or error-prone server responses and lots of low-value or duplicate URLs competing for crawling.