When using a Dictionary<TKey, TValue> as the ItemsSource for a ListBox the ListBox does not display any items and does not report an error. WPF w/ .NET Framework 4.8 allows this use.
When binding to a Dictionary directly WPF uses ToString for the Dictionary entry. You can use the Key or Value from the dictionary in the list, as well:
<ListBox
ItemsSource="{Binding DataDictionary}"
DisplayMemberPath="Key"
SelectedValuePath="Key"

I tried using ListView with GridView as a workaround, but the data binding there also does not appear to be able to use a Dictionary.

I have a workaround for this, which is to use an IValueConverter to convert the Dictionary to a List<string>.