How do you backup iPad device and data to an external hard drive?

This support page outlines the natively supported backup methods for iPad and iPhone:

How to back up your iPhone, iPad, and iPod touch - Apple Support

Native iOS/iPadOS backup and restore processes are dependent upon iCloud, or connection to either Windows PC (with iTunes for Windows installed) or a Mac (with iTunes or Finder - as appropriate for the installed version of macOS).

Natively supported methods offer full system backup - consisting of data and device settings.

How to back up your iPhone, iPad, and iPod touch - Apple Support

It is possible to use a third-party App to backup data (but not device settings) to a variety of external storage options - including third-party Cloud services, external media devices and network storage. One App that comes readily to mind is FileBrowser Professional by Stratospherix:

https://apps.apple.com/gb/app/filebrowser-professional/id854618029

You would be well advised to review the extensive online Manual and help files to determine suitability for your needs.

https://www.stratospherix.com/products/filebrowserprofessional/filebrowser-professional-user-guide.php

If your iPad Pro has a Lightning port, you will need to use an Apple Lightning to USB3 Camera Adapter to connect USB devices to the iPad. This adapter has both a USB 3.0 Type-A connector and an additional Lightning port to supply power, from your Power Adapter, to both the iPad and connected device. The Power Adapter must be rated at 12W or more.

• Lightning to USB 3 Camera Adapter

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

If instead you have one of the newer iPad or iPad Pro models, with a USB-C connector, you may need to utilise a powered USB hub (i.e., it has its own source of power) - connecting both the iPad Pro and the storage device to ports on the hub. The external storage device will obviously require an appropriate USB3 cable to connect to the USB port of the Lightning to USB3 Camera Adapter, or USB hub if used.

Some additional information can be found here:

Connect external devices or servers with Files on iPhone - Apple Support

https://www.imore.com/how-use-external-hard-drives-your-iphone-or-ipad

Well as far as data goes, it’s mainly just files that you can put on an external hard drive and you can do that through the files app.

However, if you would like to backup your iPad on a computer you can do that. You would do that through iTunes on a PC or through the finder on MAC when you plug it in you’ll get an icon you can click on and control the backup there. Really isn’t a way to back it up directly to an external drive.