Why is Google Search Console showing pages as Crawled – currently not indexed?

Community question: See the title above for the specific issue and context.

Practical answer

Google crawled this URL but did not add it to the index. Use URL Inspection to verify the HTTP status, canonical URL and indexing directives. Compare the page with similar pages and improve unique, useful information and relevant internal links. Keep only canonical indexable URLs in your sitemap. Request indexing after meaningful improvements; inclusion is not guaranteed.