During the latest webmaster hangout, Google employee John Mueller answered a question about whether Google could crawl pages with infinite scrolling.
Google has limits on how much infinite scrolling it can handle, says SearchEngines. Googlebot can render all or most of the page:
When we render the page, we use a fairly high viewport, as if we had a very long screen. And we render the page to see what it will show.
At the same time, Googlebot cannot always process the entire page. It depends on its length and how infinite scroll is implemented, notes NIX Solutions.
The best way to find out how much of a page Google is able to crawl is to use the URL Inspection tool. It renders the page the way Google sees it. With this information, you can figure out what changes are needed.