Google announced this month that over half of the pages shown in its global search results are from Google’s mobile-first indexing procedure. In mobile-first indexing, Google looks at the mobile version of your site and crawls it first, before indexing the desktop version.
If the content and structured data on your desktop pages are different from your mobile pages, your rankings may be impacted. Google says you should pay close attention to the structured data and alt-text for your images with this change.
According to Google, the platform will typically notify you when your website has moved to mobile-first indexing within Google Search Console. Therefore, it’s critical to check your messages and stay up to date.
Sources: Search Engine Land; Google Webmaster Central