Google reminded webmasters that starting September 1, it would stop supporting the noindex directive in robots.txt. The search engine sent a message about this in July through notifications in the Search Console.
Google Webmasters Tweeted “Just a reminder that September 1 is coming soon. The noindex directive in robots.txt will no longer be supported. Use the other options mentioned in our blog.“
In particular, as a replacement for noindex in robots.txt, Google advised using noindex in the robots meta tags, 404 and 410 codes, password protection, the URL removal tool in Search Consol, disalow in robots.txt.