What does "main screen" actually refer to, in battery usage?

Solution 1:

From https://www.apple.com/batteries/maximizing-performance/#ios:

Home & Lock Screen. This indicates that the Home screen or Lock screen was displayed on your device. For example, the display was awakened by pressing the Home button or by a notification.

  • If an app frequently wakes your display with notifications, you can turn off push notifications for the app in Settings > Notifications. Tap App and set Allow Notifications to Off.