I worked with a writer/editor at the Consumer Reports magazine to help them understand OSINT and cyber security risks from old, unused online accounts. They wrote a great, easy-to-digest article that you can find https://www.consumerreports.org/digital-security/how-to-find-old-online-accounts/
Also noted this article on my company’s Spotlight Infosec web site https://www.spotlight-infosec.com.