Why Some Backlinks Stay Unindexed and How to Get Them Into Google
https://theseoledger.capitaljays.com/posts/why-some-backlinks-stay-unindexed-and-how-to-get-them-into-google
Some backlinks never get indexed because of low authority, noindex tags, or being buried in blocked pages. To get them into Google, check for crawl errors in Search Console, request indexing via the URL inspection tool, and ensure the linking page is itself indexed and passes link equity.