For ListBox the datacontext is correctly identified, but for other collections (I only tested ItemRepeater and DataGrid), it will not correctly reflect the content type.
Sadly, the plugin has nothing to do with the editor highlighting. Please open an issue on the ReSharper issue tracker: it is Avalonia-aware and should properly work with its XAML.
For ListBox the datacontext is correctly identified, but for other collections (I only tested ItemRepeater and DataGrid), it will not correctly reflect the content type.