Apple's Pass Designer lets you see exactly how a pass will look on iPhone and Apple Watch
Apple Pass Designer
Apple has introduced Pass Designer, a new tool that simplifies creating and previewing Wallet passes for any business, from a local gym to a global airline. It offers templates, real-time previews using the same rendering as iOS and watchOS, and supports semantic tags for features like Siri Suggestions and Maps. The beta requires macOS 27 or later and is available for download.
The preview uses the same rendering as iOS and watchOS, so what you see in Pass Designer is exactly what customers will see on their device.