The iPad has three primary things you need to do to backup as much data as is possible. 

0. Step Zero - Store things on Google drive. Then you don't need to back them up. They are not stored on your iPad. 
 

1. Configure your Apple ID to backup your iPad data.

• Open Settings and navigate to iCloud:
  Go to Settings > [your name] > iCloud. 
• Enable iCloud Drive:
  Tap on "iCloud Drive" and toggle the switch to the "on" position. This will allow your files and folders to sync with your iCloud Drive. 
• Choose which apps and features to sync:
  You can choose which apps and features sync by going back to the iCloud settings and toggling the switch for each app or feature you want to sync. For example, you can enable "Sync this iPad" for Photos, Contacts, and Messages to sync them to iCloud. 

2. Login to Notability to backup your notes. 
Notability has two ways that it seeks to keep your data safe. The first is to set up iCloud sync. This will store your data in Apple iCloud service. This is tied to your Apple ID. The second way is with a true on-way backup of the data. You must go do the following:
 

• In Notability's Library, tap .
• Tap Connected Services
• Enable Auto-Backup
• Tap a cloud service to select it:
  • Google Drive
    Be sure the service is connected and Auto-Backup is enabled. 

3. Check other third-party apps. Some have ways to store data in iCloud, Google drive or other cloud service providers. Other apps will let you save the artwork or data as photos. Some apps only have an option to "share" files and you might need to email them to yourself. Some have no capacity at all to backup data. It is your responsibility to check these things.