Regrettably you are always going to struggle with an iPad that has so little internal storage. The 32/64GB devices are primarily intended for use in Educational settings, or in environments where the ability to store local data on the device is not required.
System storage includes a lot of cached data. Reported System Data can be expected to fluctuate as you use your iPad, the iPad automatically and optimally managing its available system resources to improve overall performance.
The only element of system storage that you can directly influence is perhaps your browser caches - which you can manually clear if you wish to do so.
For Safari:
Settings > Safari > Clear History & Website Data
For other browsers, you’ll need to find the relevant section of the App settings - which may be within the App itself.
Otherwise, transient system caches can be significantly reduced by performing a forced-restart of your iPad - although caches, by their nature, will again accumulate and be automatically managed by the operating system.
It is generally recommended that you maintain at least 4-6GB of free space at all times - as your iPad needs some temporary space to complete many tasks. When performing system software updates, you may temporarily require more.
If your internal storage is full, or is insufficient for the task that you need to perform, your only option is to better manage the storage that you have - and delete unused Apps or unneeded data.
These support pages should prove to be helpful:
About storage on your device and in iCloud – Apple Support
What's the difference between device storage and iCloud storage? – Apple Support
Manage your iCloud storage – Apple Support
How to check the storage on your iPhone, iPad and iPod touch – Apple Support
Clear Other storage on your iPhone or iPad - Apple Support
“Offloading” Apps can be a helpful method of creating temporary space for a software update:
https://9to5mac.com/2020/01/21/how-to-offload-apps-in-ios-to-save-space-without-deleting-their-data/
Additional information about creating sufficient space for installation of a software update can be found here:
If you need more space for an update on your iPhone, iPad, or iPod touch - Apple Support
External storage options can often help with managing limited internal storage. Depending upon your iPad model, the iPad will either have a Lightning or USB-C port - and may therefore require either an Adapter or USB hub to connect the USB Storage device. If your iPad has a Lightning port, you’ll need an Apple Lightning to USB3 Camera Adapter:
- Lightning to USB 3 Camera Adapter
https://store.apple.com/uk/xc/product/MK0W2ZM/A
