If I had to compare it to something, it would be like the warnings you get in the Chrome browser when you're about to navigate to a dodgy link. Android Safe Browsing works similarly by tapping into Google's extensive database of known threats. At the moment, no apps appear for me under supported apps, suggesting that — as per Mishaal's observations — this requires apps to utilize the "SafetyNet" Safe Browsing API, which lets apps determine if a URL has been marked as a known threat by Google.
Image Source: Phone Arena
So far, this new feature has been spotted by navigating to Settings > Security & privacy > More security & privacy on Pixel devices and Settings > Security & Privacy on Samsung Galaxy devices. However, the roll-out seems to be phased and controlled by Google's servers, which would explain why not everyone has it yet.
Although this seems like a feature every Android phone should get, it is currently unclear whether this will a Pixel and Galaxy exclusive. Right now it looks like most phones using Google Play Services should eventually get this update, not just specific devices, so exclusivity is hopefully not an issue.ncG1vNJzZmivp6x7sbTOp5yaqpWjrm%2BvzqZmp52nqHyou86go55loqS5rbXNoGSoraRirq95wKebq6eZmXq0rcWeZJuqn6zAqrrGZp2emaSqv6Z5xaipZpmgpcBuu81mnpqkka3Gbq3NnWSpoaiauW6wxK%2BgnJ2jlLalfZRuanFr