App name not available in some locales, but no conflicting app found

Hi, I have ported an app that I had published in Google Play Store for Android to iOS and OSX, and it is already published in the App Store with UK, Spanish and Catalan store localizations. Now I wanted to add some more localizations, such als English and Spanish(US) and German, but I get an error that the app name was used. Well, it is used, by me, apparently by nobody else. Of course I do not have a trademark for this, since it is just a little project, and there had been a free open source command line game with the same name on linux for 10 years as I found out a couple of weeks ago, so I doubt it could be trademarked by someone. How do I find someone to talk to to sort this out? I already have one person who got the app through the German App Store but without German store localization, so this message is very confusing. The app itself is not that important, I wrote it mainly to get experience with SwiftUI, contemporary Apple OS flavors and learn how to handle apps in the AppStore so when I am going to produce something larger I know what to do, how and in what sequence... So yes, I know I may just put a slightly different name there, but I want to understand what exactly is going on there.