App Clips are optional features. You can submit your app for review without an App Clip.
From App Clips:
An App Clip is a lightweight version of your app that offers users access to some of the app’s functionality. A coffee shop app downloaded and installed from the App Store, for example, might provide a user the ability to order a drink, save favorites, collect rewards, get special offers, and so on. The coffee shop App Clip only offers the functionality to order a drink.
Users find an App Clip by performing an invocation; for example, by tapping a location-based suggestion from Siri Suggestions or by scanning an App Clip Code. After the user confirms the invocation, the App Clip launches instantly, helps the user perform an everyday task as quickly as possible, and only stays on their device for as long as they need it. When a user installs the corresponding full app for your App Clip, the full app replaces the App Clip. From this moment on, confirming an invocation launches the full app instead of the App Clip, and the user gets the functionality of the App Clip within the full app. If they don’t install the full app, the system automatically removes the App Clip after a period of inactivity.
Again, consider the coffee shop’s App Clip: When a user walks past the coffee shop, the system displays a location-based suggestion from Siri Suggestions on their device. They tap the suggestion, confirm the launch of the App Clip on the system-provided App Clip card, and instantly use the App Clip to order a drink. After the user completes the order, the App Clip recommends its corresponding app to them, and they download the app. The next time they tap the location-based suggestion, they launch the full app instead of the App Clip. If they don’t install the app, tapping the suggestion and confirming the invocation continues launching the App Clip.
App Clips provide a polished user experience that helps users solve a real-world task as quickly as possible. Additionally, App Clips don’t appear on the Home screen, and users don’t manage them the way they manage full apps. Instead, the system removes an App Clip from a device after a period of inactivity, making a polished user experience even more important.