What is the latest in terms of how Google / GoogleBot sees the content on your full page. Now when it comes to lazy loaded content, John Mueller said GoogleBot tends not to watch out for a scroll event or a click to load more button. With this set up, lazy loaded content, he said you will want to make sure to set up intersection observer so Google can use that to find your content.
This came up in Friday's video around the 34:30 mark where John from Google recommends you use the intersection observer which is a Chrome API, this lets you know which parts of the page are visible at the moment. This is something GoogleBot uses when it renders the page. John explained that GoogleBot will use a super tall viewport, like really tall, and Google then gives the page time to load the content that would be visible.
So you need to ensure that the content is visible and loadable in that viewport, that is the "more guaranteed way" of ensuring indexing of that content, John Mueller said.
The other way is where Google has to watch out for a scroll event or a click to load more button and John said something like that is "usually something that GoogleBot tends not to do."
So in particular, John said, it is not something Google knows where which elements to click on to see if something would load. "So that's something where probably we would not be able to pick up that content," John Mueller said. "But if you use intersection observer probably we would be able to," he added.
To be clear, this is for content that does not load when the page is accessed. Instead, this specific advice is for pages that have its content load based on scrolling down the page and/or clicking on specific objects on the page.
For more on the intersection observer, see over here.
Here is the video, you may want to scroll back a bit more to get more context but I wanted to start you in a place where it takes you the least time to get the message:
Forum discussion at YouTube Community.