Hello Thegrog,
"System Data" or "Other" can include a lot of different things like system files, software updates, Siri voices, cached files, logs, just to name a few. Your iPad should automatically remove these cached files and temporary files if it needs more space.
You can find more information about this here: How to check the storage on your iPhone and iPad - Apple Support
If you have recently restored the iPhone or signed into iCloud we would suggest waiting an additional 48 hours. This allows the iPad to take a look at all the files and get rid of the ones it no longer needs. Be sure it is connected to Wi-Fi, and power, as much as possible during this time period.
If the issue continues, be sure the iPadOS is up to date:
1. Back up your device using iCloud or your computer.
2. Plug your device into power and connect to the internet with Wi-Fi.
3. Go to Settings > General, then tap Software Update.
4. If you see two software update options available, choose the one that you want to install.
5. Tap Install Now. If you see Download and Install instead, tap it to download the update, enter your passcode, then tap Install Now. If you don't know your passcode, learn what to do.”
Additional information is available at Update your iPhone or iPad - Apple Support.
If the problem remains, follow these steps:
- Back up your device with iCloud or a computer.
2. When the backup is complete, go to Settings > General > Reset > Erase All Content and Settings.
3. When asked, choose Restore from Backup and choose the most recent backup.
4. Wait for the restore to finish. Then go to Settings > General > Software Update, and install the latest version of iOS.
5. You might see the Home screen before the restore is complete. Wait for the restore to complete before you update your iPhone. You can check the restore progress in Settings > [your name] > iCloud > iCloud Backup.
6. Do not install new apps, or download or stream music or videos until the the iPhone is updated.
Have a good day.