Could not be updated. An unknown error occurred

These models of iPad are capable of update to iPadOS 26 - at the time of writing, iPadOS 26.2 being the current production version:

• iPad Pro 13" (M4/M5)
• iPad Pro 12.9" (3rd generation and later)
• iPad Pro 11" (1st generation and later + M4/M5)
• iPad Air (3rd generation and later + M2/M3)
• iPad (8th generation and later + A16)
• iPad mini (5th generation and later + A17 Pro)

Notwithstanding my earlier reply concerning error #1109, these support pages outline both the available methods by which a supported update can be performed - and additional troubleshooting should you experience difficulties:

Update your iPhone, iPad or iPod touch – Apple Support

If you can't update or restore your iPhone, iPad or iPod touch – Apple Support

If your iPhone, iPad or iPod touch won’t update - Apple Support

iOS update and restore errors – Apple Support

Be aware that while an iPad may be capable of update, in some circumstances you may need to use a computer to perform the update*. To do so, you will need access to either a Windows PC (with iTunes for Windows installed - or the more recent Apple Devices App) or a Mac (with iTunes or Finder - as appropriate for the installed version of MacOS). Ensure that your installed version of iTunes has been updated to the most recent version; the essential device drivers are included.

Download and use iTunes for Windows – Apple Support

Update to the latest version of iTunes – Apple Support

Update software on iPhone, iPad or iPod touch in iTunes on PC - Apple Support

Update your iPhone, iPad, or iPod touch with the Finder - Apple Support

Apple Devices App (Windows PC):

https://apps.microsoft.com/detail/9np83lwlpz9k?hl=en-ms&gl=MS

(*) If you don’t have access to a suitable computer of your own, that of a helpful friend or family member will suffice. Alternatively, the technicians at the Genius Bar of your local Apple Store or Apple Authorised Service Provider (AASP) will be delighted to assist.

Genius Bar Reservation and Apple Support Options - Apple

If you have a beta profile installed, ensure this has been removed from your iPad - as, otherwise, installation of production software updates may be inhibited. This support page provides the necessary information to remove the beta from your iPad:

How to uninstall iOS beta software - Apple Support

You should note that for your iPad to install an available update, its battery must be charged to at least 50% capacity - and/or be connected to its Power Adapter. Similarly, the iPad can only be updated over a standard WiFi connection - or be updated by a PC or Mac using iTunes or Finder - over a USB connection.

First we need to verify that your iPad is eligible for an update. Please tell us which model iPad to you have? And what is its current OS? The link below may help.

Identify your iPad model - Apple Support

This Apple Support page details error #1109:

If you see Error 3194, Error 1109, or other network connectivity errors when restoring your iPhone or iPad - Apple Support