We are developing an app with different versions for iOS, iPadOS, and MacOS. There is no shared code, but they do sync together. Can we give them all the same name? A few other points:
Your project in Xcode can have multiple targets, e.g. iOS, macOS, watchOS etc. so you should be able to have one project with multiple targets, each with their own code. You then build and distribute this as one app with one name.
When a user launches it on macOS, the macOS target launches. When they launch it on an iPhone the iOS target is launched.
For example, I have an app with an iOS and watchOS targets. They're in one Xcode project with one name, and they just launch the appropriate binary on the correct platform.
Sorry if I've misunderstood your issue, but this does seem to be quite simple, no?
In App Store Connect you create one app. Within that app you setup multiple platforms. Each platform gets its own binary, app description, app screenshots, etc. But all use the same app name. Though I don’t know if you can setup different binaries for iOS and IPadOS. My own app supports both iOS and IPadOS with one binary and then macOS with another.