Unable to customise lock screen on my iPad running iOS 16.7

The first generation iPad Pro was introduced by Apple in 2015. As you very likely know, iPadOS 16.X is the latest version supported by this iPad.

You appear to be trying to use features that were not introduced until iPadOS 17, and are therefore not available to you.

Brabzz wrote:

I have the 2016 model

That is, as you said, a first generation iPad Pro which was introduced in 2015.

and I know it was added in 16 not 17

The new features in iPadOS 16 were associated with these topics:

• Stage Manager
• iCloud Shared Photo Library
• Freeform
• Messages
• Mail
• Focus
• Weather
• Safari
• Visual Look Up
• Live Text
• Home
• Family Sharing
• Accessibility
• Photos
• Privacy and Security
• Notes
• Reminders
• Stocks
• Memoji

That's it.