Google has made two changes in Google search console in the last 24 hours. Most significantly, the index coverage report now uses mobile-first indexing data when it is available. Meanwhile, Google has issued notices about sunset for new Google search console reports when similar reports exist in the new Google search console.
Google index coverage report uses mobile first indexing data. Google has already updated its Index coverage report to use data from mobile-first indexing initiatives rather than using desktop indexing data for sites that have been switched to mobile-first. Google said that this only affects "the properties that mobile has migrated to the first index."
What has changed in the Index coverage report? Google said that the only data affected in this report is related to "error calculations" and "new issues" related notice. Moving forward, this index coverage report will reflect the mobile-first indexing position around those issues. Google said that "indexed page counts by this change are not affected."
When did the index coverage report change? Beginning and moving from November 26, 2018, it has changed to the properties which have already been moved to the mobile-indexing initiative, Google said. You will know whether you will move because Google will send you a notice that your site / property has already been moved. If not, Google is still using Desktop Indexing Data for this report, until a notice has been moved to your site.
Google has drop some of the old reports. Google has posted a notice in the old version of Google Search Console, so users know that some reports are being removed. Search Analytics reports, Rich Reset Report, AMP Report, Link Report, Internal Link Report, Manual Action Report, Mobile Usability Report, Index Status Report and Crawl Errors Report, are currently available in the old Google search console. All these reports will be removed sometime in the future. Google has not given us a date.
Notice: "Important: This report will soon be replaced by the new search console. Please update your links to point to the new search console." Some instructions link to a new version of the Google Search Console with a direct replacement report.
Why does it matter? With the change of index coverage report, if you see changes in errors around November 26 and your site is moved to mobile-first indexing, Google may be related to how these reports are reported. It does not affect your ranking, but it affects the index coverage report. It's just a reporting change and has zero impact on your current rankings.
On Google's notice about Google removing older reports in the Google search console, Google said that they are currently only removing the reports that are changing to the new version of Google Search Console. In some cases it may mean how you should use a new report or change your day-by-day everyday and start using a new report on the old. But overall, Google said that you should be able to get the data you want from the new reports. It will only take time to learn how to use it.