How it discovers and cites pages
AI Overviews are generated on top of Google's main search index using the Gemini family of models, so the pages eligible to be cited are essentially the pages Google already ranks for the query. The Overview summarizes across several top results and links out to the supporting pages. Controlling whether your content feeds these summaries is done with the Google-Extended token in robots.txt, separately from normal Googlebot indexing.
What this means for getting cited
To be cited by Google AI Overviews, your page first has to be reachable through the index it draws on (Google Search) and crawlable by the relevant bots, then it has to answer the user's question clearly enough to be quoted. I test exactly these variables at HZ and publish what moves the needle.