Google Chrome for iOS now allows you to lock Incognito mode behind your iPhone’s Face ID authentication feature so that only you can access the open tabs. Google is still testing this feature, so you have to enable it via the chrome://flags page. Every time you try to access the secured tabs, the browser will prompt you to unlock them with Face ID. To disable the feature, simply toggle off the ‘Lock Incogenito Tabs WhenYou Close Chrome’ in the settings.
Source: https://www.bleepingcomputer.com/news/google/google-chrome-on-ios-is-getting-an-enhanced-privacy-feature/