Troubleshooting the Drop in Ranking of the Website After Mobile-First Indexing Is Enabled

The same structured data with correct URLs is present in the mobile and desktop version of the website.The ‘noindex tag’ blocks a mobile web page from indexing. The mobile version of a web page does not have all the images as desktop version of the web page has.

Source :- https://developers.google.com/search/mobile-sites/mobile-first-indexing