Legal and age-verification interstitials can affect crawling
Interstitials (for example, those that require users to verify their age before browsing) can have a negative impact on crawling and indexing if not implemented properly. Googlebot doesn’t click buttons or fill in forms, so any interstitial that requires those actions before the page is loaded may prevent Googlebot from crawling the content itself. Ideally, it’s recommended to use JS/CSS to display interstitials on top of existing content that’s already been loaded in. Because the content is still being loaded and users can access it after navigating the interstitial, this would not be seen as cloaking.
Google Differentiates Between Legal & Advertising Interstitials
Google will generally try to recognise legal interstitials and banners in order to differentiate them from advertising banners. This is to done to prevent them from causing problems when Google crawls the site. The only time this may become an issue is when the interstitial replaces the content on the page and prevents it from being crawled.
Check For Interstitials With Google’s Mobile-friendly Test
Interstitials may seem like a quick win for sites, but they cause long-term UX issues. Check your site for interstitials with Google’s Mobile-Friendly testing tool.
Use Flexible Sampling or First Click Free to Allow Google to Crawl Content Behind Paywall
For pages with a single sign-on interstitial or behind a paywall, John recommends implementing flexible sampling or a first-click free approach so that Googlebot can crawl these pages.
Legal Interstitials Which Redirect Users May Block Google
Googlebot Can’t Index Content on a Page With an Interstitial
Page Layout is Only an SEO Issue for Mobile-Friendly Testing
Page layout is only really an issue for SEO when it comes to mobile-friendly testing and the mobile interstitial update.
Pages That Redirect to Interstitials Are Dropped from the Index
Make sure pages don’t redirect to interstitials and that they’re kept on the same URL or Googlebot could drop these pages from the index.
Mobile Interstitial Penalty Doesn’t Impact Brand Searches
The mobile interstitial penalty doesn’t have any impact on desktop results, and won’t impact brand searches. Using banners within the page are a better option than pop-ups which prevent any content being seen by users.