5th generation iPad not detecting USB audio accessory

What, specifically, are you attempting to connect to your iPad5?

As your iPad5 has a Lightning port, to connect USB accessories you will need an appropriate adapter - a Lightning to USB3 Camera Adapter being recommended:

• Lightning to USB 3 Camera Adapter

https://store.apple.com/uk/xc/product/MK0W2ZM/A

This adapter contains an Interface converter, USB 3.0 Controller and USB Root Hub - presenting a USB 3.0 Type-A connection to which you may connect many (but not all) categories of USB devices. USB Device support by iPad is generally limited to Mass Storage devices, basic HID devices (such as wired Keyboard and basic Mouse) and some audio. 

Does the adapter you bought state any operating system requirements. The iPad 5 is incapable of running any higher iPadOS version that is 17 or higher.