Hello Kanye West,
there are four methods/tools that I know of that expose hidden backlinks.
1. Google query: "competitordomain.com" -site:competitordomain.com. You can be sure that a PBN is not only referencing keywords which the money site should rank for but also the domain name of the money site. Install a user agent switcher plugin for your browser (like this one for FireFox:
https://addons.mozilla.org/de/firefox/addon/uaswitcher/) and add the ahrefs UA to it (you can find it here:
https://user-agents.net/bots/ahrefsbot). Now visit every page on the SERPs and check it with your browser/Googlebot UA and ahrefs UA. If a page blocks ahrefs but not your browser/Googlebot UA it is probably but not necessarily a PBN page.
2. Google query automation tool:
https://www.blackhatworld.com/seo/free-pbn-hunter-find-your-competitors-hidden-pbn.863130/
3. Bing Webmaster Tools Method:
https://www.blackhatworld.com/seo/g...bn-backlinks-of-any-website-for-free.1311731/
4. A hidden backlink checker
I prefer #4 because of data precision and usability but #1-3 are free which is an advantage.
Sincerly,
The Data Scientist