As your iPad9 has a Lightning connector, to connect USB storage and other devices you will require an Apple Lightning to USB3 Camera Adapter:
https://store.apple.com/uk/xc/product/MK0W2ZM/A
Don’t be confused by the name of this Adapter - as it is the key to connecting many USB devices to your iPad. The adapter incorporates the essential USB Controller/Root Hub that interfaces USB accessories to your iPad’s Lightning port.
You should also note that the iPad alone cannot provide sufficient power for most USB storage. The Lightning to USB3 Camera Adapter has both a USB Type-A port to connect your USB device - and also has a pass-through Lightning port, to which you must simultaneously connect your Power Adapter (rated 12W or greater).
More information can be found in the iPad User Guide - along with other frequently overlooked information about your iPad and iPadOS:
Connect external storage devices to iPad - Apple Support
To be recognised by iPadOS, the attached USB storage device must be formatted to FAT, FAT32, exFAT, APFS or HFS+ with a single partition. Microsoft NTFS and other proprietary device formatting are not supported. Formatting and partitioning, if required, must be performed using a separate computer; iPad does not provide any facilities to format an external storage device.