I have the same issue. My app is only in Testflight and hasn't been published to the AppStore ever. So I cannot use the "Transfer App" feature. On the other hand I cannot delete the app id and I am stuck. I have to basically use a new app id which leads to many other changes because the bundle id is used in many many places - third party sdks, dashboards, backend services etc.... this is very very bad.

Same problem here. I have a test app which is not published on the app store, now I want to remove it from the account but the AppID cannot be removed.