Nevermind. The 'Storekit External Purchases or Offers capability' and the corresponding entitlement 'com.apple.developer.storekit.custom-purchase-link.allowed-regions' mentioned above are indeed only for Payment options on the App Store in Japan. The reason for the confusion is that after we signed the 'Alternative Terms Addendum for Apps in the EU' this was the only capability that showed up as 'external purchases', due to a different bug that we are currently trying to solve with support.

As a company, you can pick the publisher name when you add your first app. If you regret your choice, you can contact support and ask them to change it to the business license name only, can't choose something else. This is based off a support ticket I had last June.