Google finished the process of moving sites across to mobile-first indexing. John Mueller confirmed on Mastodon that the company had now moved across the last batch of sites eligible for mobile-first indexing.
Writing in response to a question from Search Engine Land’s Barry Schwartz, Mueller said there were a tiny handful of sites left, which didn’t really work on mobile. These will remain on desktop indexing.
Google began switching sites to mobile-first indexing back in 2018. Google’s original deadline for sites to be ready to switch to mobile-first was September 2020. This was then delayed to March 2021 in the wake of covid, and finally dropped altogether in November 2021 with an acknowledgment of “unexpected challenges” faced by some sites.
If your site has not switched over, it will likely never now be moved to mobile-first indexing. All new sites automatically default to mobile-first indexing.