You can purchase Plenary premium to support the app development. Premium will give unlock many features such as

- Pure black theme

- Automatic cloud backups

- Ability to directly open specific links in another app

- Unlimited feeds

- Quick actions in notifications

- Internal YouTube player

- More accent colors

- More fonts for reader screens

You can be get premium features by purchasing Plenary lifetime premium or subscribing to any of the subscription plans (monthly, quarterly or yearly)