Last day, there was a bunch of Google Search Console notifications around the websites that were making the switch to mobile-first indexing processes. You need to keep in mind that you are already in the mobile-first indexing process for quite some time by the time the notification reaches you.
John Mueller from Google validated this occurrence on Twitter. He said that the switch happens before and the messages are sent later on.
Google need not stop sending the notifications are they are really useful. But the notifications come delayed by a week or more than that when a site transitions to mobile-first indexing process.
It is still time before Google starts to move all of the websites to the mobile-first indexing process.
See the forum discussion at Twitter.