Google is now doing mobile-first indexing for over half of the pages in search results. With mobile-first indexing, Google crawls the web pages from websites with the smartphone Googlebot instead of the desktop Googlebot.
John Mueller, Webmaster Trends Analyst at Google, wrote that in general, Google move sites to mobile-first indexing when the tests assure Google that websites are ready. All publishers are being notified of the transition through a message in Search Console.
Publishers can see on Search Console what is the Googlebot that is crawling a web page running the URL Inspection tool. Here an example: