A previous submission for this app was released with a Windows 10/11 .msixbundle or .appxbundle. Subsequent submissions must continue to contain a Windows 10/11 .msixbundle or .appxbundle.

What it means

Once an app has been published with an .msixbundle or .appxbundle, every later submission has to contain a bundle too. A Microsoft moderator checked with the Store team and there is no way to change this rule. Developers run into it after moving a UWP app to WinUI 3, when Visual Studio starts making a single .msix.

Renaming or zipping an .msix doesn't make it a bundle. Partner Center still rejects it.

How to fix it

1. Build an .msix for each architecture you support, all with the same identity and version.
2. Put them in one folder and make a bundle with MakeAppx, which comes with the Windows SDK:

   MakeAppx bundle /d "C:\My Files" /p MyBundle.msixbundle

   Microsoft says every package in a bundle must use the same manifest elements and attributes, except ProcessorArchitecture, and the bundle version's last number must be 0.
3. Upload the .msixbundle on the Packages page.