You can look at the Samsung T5 portable SSDs.
These work with iPads running iPadOS.
In addition, You need to purchase the actual, genuine Apple Lightning to USB-3 camera adapter, from Apple, and plug that
adapter into external power using your iPad charge cable and Apple power/charging block!
https://www.apple.com/shop/product/MK0W2/lightning-to-usb-3-camera-adapter?fnode=37
You NEED TO PURCHASE THIS EXACT genuine Apple adapter above!!!
This is THE ONLY adapter that works!
Cheaper ( cheap in price and quality ) third party, “knockoff” adapters WILL NOT WORK!!!!
With Lightning connector equipped iPads, you need this adapter as it has a Lightning connector power connection
to power both the iPad and to connect a commonplace USB flash memory drive or portable SSDs.
Without the additional power to the iPad, USB flash drives and portable SSD drives will NOT work with older iPads with the Lightning connector.
The Lightning connector alone cannot convey the,necessary power requirements needed for normal USB style flash memory drives or other types of drives!
YOU NEED TO CONNECT AN EXTERNAL POWER SOUCE TO THIS ADAPTER for that adapter to work with ANY externally connected drive!!! Even to get any standard USB flash memory drives to work on older Lightning connector equipped iPads.
There are lots of YouTube videos that discuss and demonstrate this.
In addition the external drive needs to be formatted, by a Mac, into one of these file/data formats
APFS
FAT32
exFAT
Drives formatted in NTFS will NOT work with iPadOS.
Good Luck to You!