When implementing the large content viewer, UIKit components will usually have a large content title and image configured for you. But if you are developing a custom component, or you want to add info to a native component, you can do so.

Slack app. There is a floating button, with a notepad with a pencil icon, to compose new messages. If you tap and hold, it shows the large content viewer in the middle of the screen, with both the icon and some text that reads