If you search for Cristiano Ronaldo on Google, one of the search results is his Instagram page. When you click on that search result, you are met with a login wall (at least on desktop). You cannot view any details from an Instagram page without logging in first, as reported here and here and here.
I thought that Google did not show search results that link to pages behind a login wall. Is my understanding incorrect? How does Instagram convince Google to show its pages in search results, despite the login wall?
The reason that I'm asking is that I am considering developing a login wall for my own website that I am developing. It is important to understand how would treat a website with a login wall.