Navigate to Backup in Settings
Press Recovery Code and generate a new 12 word key. This key will be used to unlock the backup file if you need to restore. Write the words on a piece of paper, take a photo, or a screenshot.
Configure a backup location. The phone itself, a plugged-in usb drive, or Nextcloud. To use NextCloud - Open Settings, Search for Accounts, Add account, Nextcloud.
The backup location will initilize then you're ready to go!
Enable backup my apps. Click the 3 dots at the top right and press "Backup now".