Google announced back in March that it would be changing over to ‘mobile first indexing’ later in the summer. Now it’s put that date back to March 2021, apparently because the pandemic may have made it harder for some websites to prepare for the change.
The chances are that your site is already being indexed ‘mobile first’ – the majority of the web is being indexed this way by Google. This means that the search engine will crawl your site pretending to be a mobile device, because the majority of Google searches are now on mobile devices. If your site shows different content to different devices, it’s the mobile content which will be in the Google result. If your content is the same on all devices, it won’t matter.
All that Google’s announcement is doing is setting a date for the changeover to be completed. You can check in Google Search Console how your site is being indexed.