Hi, I need help backing up my iPad to an external drive

At present, native iOS/iPadOS backup and restore processes are dependent upon iCloud, or connection to either PC (with iTunes installed) or a Mac (with iTunes or Finder - as appropriate for the installed version of macOS). The native support options for iOS/iPadOS also do not extend to using theMac-native Time Machine - this also being Apple proprietary.

More information about supported native backup methods are outlined here:

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

Backup methods for iPhone, iPad, and iPod touch - Apple Support

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

It is possible, however, to use a third-party App to backup data (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

See Backup methods for iPhone, iPad, and iPod touch - Apple Support

Options are to backup to iCloud, or to a computer (Finder on a Mac, iTunes on a PC).