After 3 years after mobile-first indexing announcement, Google declared that new websites generally are ready for this method. After July 1, mobile-first indexing was applied by default for all domains previously unknown to the search engine.
Now, when crawling a website and its subsequent ranking, the mobile version of the website will be primarily taken into account. You can check your website for compliance with these conditions using the URL Inspection Tool. This allows you to check how the website was last crawled and indexed by Googlebot.
Pages of older websites will continue to be evaluated for readiness for new indexing, and they will receive a notification through the Search Console as soon as the search engine finds them ready. Since the indexing of new websites is performed by default as mobile-first, they will not receive additional notifications.
Google’s guidelines for providing indexing of mobile versions remain relevant for both new and old websites. Their readiness is calculated
based on several factors:
content (text, media, links);
other metadata (titles, descriptions, meta tags, etc.)
We recommend passing this checklist if you have recently launched, redesigned or significantly changed the structure of the website. Read more about the importance of preparing your website for mobile-first indexing in this article.
Although the support of responsive web design, dynamic serving, and separate mobile URLs for mobile websites will not end. This is still preferable for new websites to use responsive web design for better search engine optimisation. Because of the perpetual confusion that arises with separate URLs, Google recommends using a single URL for both desktop and mobile versions.