Google is switching its entire index to mobile-first by March 2021. In concrete terms, content that can only be seen on desktop devices is ignored for search.
This is not new information, but it should still be a final warning for anyone whose mobile site does not yet show every piece of content in full. The switch to mobile-first also means that desktop content which was indexed earlier will gradually disappear from the index.
At the latest Pubcon, Google confirmed the planned date for finishing the switch to mobile-first. Website owners therefore still have until March next year to rebuild their sites so that all relevant information (the information you want to rank for) can be found in the mobile version. That also covers comments, structured data, images and videos.
For anyone deciding on a new website right now, this deadline is obsolete. New websites have been built to a strict mobile-first approach for quite some time. Checking that once more does no harm.
Google is switching its index to mobile-first, which means websites have to optimise their mobile versions by March 2021. Anything that is only visible on desktop devices is ignored. New websites should already follow a mobile-first approach.