There is currently no way to look up app bundle IDs in the Apple iOS App Store directly. To find the identifier, you will need to look at a file inside the app.

For Apps in the App Store

  1. Search for an app in the App Store via the web - https://www.apple.com/ios/app-store/
  2. Extract the unique ID in the URL
    1. For Pages: https://apps.apple.com/app/pages/id361309726
  3. Open a new tab in your browser and go to https://itunes.apple.com/lookup?id=361309726
    1. Replace 361309726 with the unique ID found in step 2
  4. Download the file to your computer
  5. Open the file downloaded and search for “bundleId”
    1. For Pages: com.apple.Pages

Found this great tool to speed up the process: https://offcornerdev.com/bundleid.html
Apple has also documented their bundle ID here: https://support.apple.com/en-au/guide/deployment/depece748c41/web