Start here:
What does iCloud back up? - Apple Support
After you have created the initial iCloud backup, you can select which Apps and data are included within the backup.
Settings > [Your Name / AppleID] > iCloud > [Device Backups] iCloud Backup > [All Device Backups][This iPad] > Show All Apps

Simply select/de-deselect the Apps that you wish to include within the backup.
You should note that any Apps that you have enabled to synchronise with iCloud will automatically be excluded from the iCloud backup…
Settings > [Your Name / AppleID] > iCloud > [Apps Using iCloud] Show All - enable or disable as required
For example, if you have enabled iCloud Photos, your Photo Library will not be included within an iCloud backup. If iCloud Photos has not been enabled, the Photo Library will be included within the iCloud backup - unless manually deselected from the backup list.