Android's Digital Wellbeing service can be updated independently of the OS, since it's distributed through the Play Store, so Google can add new features outside of major Android releases. That has just happened, as the new 'Focus Mode' feature has finally left beta, and is heading to all Digital Wellbeing-compatible devices.
Focus Mode first appeared in the beta channel for Digital Wellbeing back in August. It allows you to select apps to pause, and when Focus Mode is activated, those apps will be greyed out in the launcher, and all notifications will be hidden. Opening a paused app requires going to the Settings and un-pausing it — not a huge deterrent, but enough to keep someone from opening Twitter without thinking.
Since the initial beta launch, Google has added a few more features. You can now schedule Focus Mode to turn on at certain days and times, so you can remember to stay off Instagram while at school or checking work emails on the weekend. You can also now take a short break from Focus Mode at any time.
Focus Mode is available on all Android devices that already have Digital Wellbeing, though it might take a short period for the update to roll out to everyone.