If you bundle your Mac build in an .app bundle with MonoKickstart, the location of your "Content" folder needs some path hacking (because it is expected to be in "macOS/resources", and standard file I/O will try to load from the executing directory). For this purpose, you should open files as much as possible with
TitleContainer, which will resolve the correct content path for you, no matter the target system (e.g.
TitleContainer.OpenStream(_content.RootDirectory + "/" + _sheetName + ".xml");).
In case you can't use
TitleContainer, you can use a hack like this:
private static string _trackPath = "Content/Musics/";
if (!File.Exists(_trackPath + "track01.xnb")) // MacOS hack if content can't be found
_trackPath = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "..", "Resources", _trackPath);
But as a rule of thumb, always use
TitleContainer for non-content file I/O.