iPadOS is a sandboxed environment - where each App has its own “space” for associated documents. If the App is deleted, the entire sandbox “space” in which it resides - along with any local data therein - is deleted from the iPad. If instead an App is offloaded, the App is removed but the locally stored data is retained on the device; offloading is useful if an malfunctioning App needs to be reinstalled.
By contrast, any App data independently stored in a Cloud location is not lost - as it isn’t stored locally. Deletion of the App will not directly impact any Cloud storage.
Depending upon your backup settings - contingent upon you iPad not having run an automatic backup since deleting the App - your data may still be safely stored in your iCloud/iTunes backup. If a backup (either manual or automatic) has run since deletion of the App, any backup data relating to the deleted App will have been purged from the backup.
iCloud Backup, if enabled, can be verified here:
Settings > [Your Name /AppleID] > iCloud Backup > iCloud Backup
Your current App backup settings can be found here:
Settings > [Your Name / AppleID] > iCloud > Manage Storage > Backups > [This iPad]
If iCloud backups are enabled, here you will see the App backup settings for each of your currently installed Apps - and the total volume of data currently backed-up for each individual App. NB: This view does not allow you to determine the filenames contained within the App backup.
Assuming that you have an iCloud backup, the entire backup can be restored to the iPad; selective backup of individual elements of the backup is not possible - as such, restore from backup is all or nothing.
Restore your iPhone, iPad, or iPod touch from a backup - Apple Support
Restoring from backup will wipe any locally stored data on your iPad - replacing it entirely with data from the backup. As such, any other data that has been locally stored/modified iPad data, since its last backup, will be lost - unless you take steps to identify and preserve this data prior to restoring the backup.
I hope this provides some helpful and useful clarity as to what is possible - and the outcome.