Markup support with different models

[jido]

My iPhone is running iOS 18, but I can’t seem to have Markup enabled. Is there a limitation on which models can use it?

Write and draw in documents with Markup on iPhone

Use built-in drawing and markup tools on iPhone to annotate documents, images, PDFs, and more.

support.apple.com

 

[Paddle1]

What do you mean by you can't? Considering it was introduced in iOS 12 it should work on any iPhone released in the past 10 years, back to the 5S.