Mobile-First Google Indexing Starting 2020 September
Google had finally announced for mobile-first indexing starting September 2020. This is because Google found that 70% of the search research are from mobile devices. Before that, Google will still crawl and index website from desktop, but near future it will prioriotize indexing mobile version of your websites.
Mobile-First Indexing refers to Google will predominantly use mobile version of the content for ranking and indexing. Google used to index based on desktop version of a website. But since majority of the users are shifting to mobile devices, indexing are done on mobile content moving forward.
If you are not sure whether you site are mobile first, head over to https://search.google.com/test/mobile-friendly to check. For more guideline, you can go to https://search.google.com/test/mobile-friendly.
In short, the traffic from mobile devices are increasing. Supporting mobile display is more relevant than ever. You will gain better visibility from users and index better from Google.