Modular VS Infograph Modular world clock. Sun rise and sun set.

Hello Kartnerd1,

It does appear that World Clock (Sunrise/Sunset) is a complication for the Infograph Modular face according to Apple Watch faces and their features - Apple Support.

According to Customize the watch face - Apple Support, complications are added to watch faces using these steps:

You can add special features—called complications—to some watch faces, so you can instantly check things like stock prices, the weather report, or information from other apps you installed.

1. With the watch face showing, touch and hold the display, then tap Edit.

2. Swipe left all the way to the end.

If a face offers complications, they’re shown on the last screen.

3. Tap a complication to select it, then turn the Digital Crown to choose a new one—Activity or Heart Rate, for example.

4. When you’re finished, press the Digital Crown to save your changes, then tap the face to switch to it.

Some apps you get from the App Store also include complications.

Watch faces can also be customized from the paired iPhone using the steps outlined here: Explore the Face Gallery on Apple Watch - Apple Support

Have a good day.