How to upgrade my Apple IPad to iOS 11

Looks likes it is not possible, you have an outdated iPad.

Most apps require iPadOS 14 or later.

Considering a newer type of iPad?

If your iPad is eligible for an update, then go to: Settings -> General -> Software Update

You can check by reading this Apple article:

iPad models compatible with iPadOS 13 to iPadOS 15.6

iPad models compatible with iPadOS 15.5 – Apple Support (UK)

Is your device compatible to update to the new version? See the article(s) below. 

iOS 12 is compatible with these devices.   *

IOS 11 is compatible with these devices   *   If you can upgrade to IOS 11, you can upgrade to IOS 12

See the articles below.

Update your iOS device.  -

Get help with over-the-air iOS updates  -

Update – Can’t or can’t restore   -

Have you tried using iTunes on a computer or Finder if running Catalina or later to do the update?

Update software on iOS devices in iTunes on Mac. -

Phone, iPad, or iPod touch - Update with Finder.  *

iPhone, iPad, or iPod touch - Update with iTunes.  *

If you see an error when you update or restore your iPhone, iPad, or iPod    *

Updating iOS: common issues and solutions.  -

ASC YouTube for  how to update your iPhone, iPad, or iPod touch to the latest version of iOS or iPadOS —wirelessly or using your computer.