This allows an app's data and settings to be restored when you reinstall the app on HTC U11+.
On phones running Android 8, these are the items that can be backed up using your Google Account:
Auto Backup periodically backs up your phone to a private folder in Google Drive. It occurs every 24 hours when the phone is idle, charging, and connected to a Wi-Fi network.
Backup data will not count towards your Google Drive storage quota. Large files or files that app developers have chosen to exclude from the service will not be backed up.