Google added screen pinning several years back, but the feature never got much attention. Screen pinning locks your phone to a single app, which is handy when you need to hand your phone to someone else and would prefer they didn't go snooping. There's a frustrating bug in Android Q beta 3 that completely breaks this feature when the new gesture navigation is enabled.
The Android Q full gesture nav option replaces the home and back button with an iPhone-like swipe zone. You probably know where this is going; you need those buttons to exit screen pinning. So, gesture mode traps you in screen pinning mode.
Since this is a beta, things can get a bit weird and inconsistent when you run into a bug like this. Sometimes, the phone lets you get back to the home screen from the pinned app, but you won't be able to access the settings or status bar. Attempting to launch other apps also fails. Other times, you're stuck in the pinned app and can't even get home. It will be interesting to see how Google addresses this incompatibility in future releases.