You need to purchase the actual, genuine Apple Lightning to USB-3 camera adapter, from Apple, and plug that adapter into 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!!
This is THE ONLY adapter that works!
Cheaper ( cheap in price and quality ) third party adapters WILL NOT WORK!!!!
With Lightning connector equipt iPads, you need this adapter as it has a power connection to power both the iPad and to connect a commonplace USB flash memory drive or portable SSD drive.
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.
There are lots of YouTube videos that discuss and demonstrate this.