1. On the iPhone's lock screen, touch and hold anywhere on the display until you see the Customize button. You'll need to ...

To pin or star a message on an iPhone ... and select "Wallpaper." Then, choose a wallpaper and tap "Set Wallpaper." When prompted, select "For This Chat." Share Your Live Location with Others ...

Also, Dark mode finally applies to all of the iPhone's home screen, with options for coloring icons and affecting the brightness of the wallpaper image. Here's how to customize the looks.