Searching for your personal information inside the Google app has been possible for a while. It first showed up as the In Apps tab back in 2016, but was later renamed to Personal and started appearing on the desktop as well, then disappeared again. But recently, Google seems to have given personal searches more prominence inside the Google app on Android by dedicating a shortcut to them in the menu and on the app icon.
We're not sure how long ago Personal Search started showing up. Odds are it's been rolling server-side for a long time to users, but we just got tipped about it and, right now, it seems to be there on every device we have in our hands.
When you open the Personal Search section, you'll see an interface similar to In Apps, but more modern. There's local relevant information from your device like your top contacts, conversations, upcoming events, recently visited pages, and recent activities on compatible apps. In my case, you'll see Todoist, one of the few apps that implemented In Apps search a long time ago. You can view more from any category, with selection bubbles letting you narrow down some results.
But you can also perform searches, and all the results will be from your own data. Searching works even when offline, and it seems that the entire Personal tab doesn't require any internet connection.
If you'd like to access this section of the Google app quickly, it has its own app shortcut, which you can break into a standalone shortcut on your homescreen. Tapping it immediately takes you to the Personal tab, where you can look through all the information on your Google account and device.
The Personal Search shortcuts and tab are showing up both on the Google app 8.19.10 beta and 8.16.19 stable, but as I mentioned earlier, odds are they've been rolling out to users server-side for a while.