a lot of work

ModpackUpdater.Apps.Manager/Utils/DictionaryValueConverter.cs

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+using System.Collections;
+using System.Globalization;
+using Avalonia.Data.Converters;
+
+namespace ModpackUpdater.Apps.Manager.Utils;
+
+public class DictionaryValueConverter : IValueConverter
+{
+    public object? Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
+    {
+        if (parameter is IDictionary dict && value != null && dict.Contains(value))
+            return dict[value];
+        return value?.ToString() ?? string.Empty;
+    }
+
+    public object ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture)
+    {
+        throw new NotSupportedException();
+    }
+}

ModpackUpdater.Apps.Manager/Utils/Extensions.cs

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+namespace ModpackUpdater.Apps.Manager.Utils;
+
+internal static class Extensions
+{
+    public static string? Nullify(this string? @this)
+    {
+        return string.IsNullOrEmpty(@this) ? null : @this;
+    }
+}

ModpackUpdater.Apps.Manager/Utils/MyFilePickerFileTypes.cs

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+using Avalonia.Platform.Storage;
+
+namespace ModpackUpdater.Apps.Manager.Utils;
+
+public class MyFilePickerFileTypes
+{
+    public static FilePickerFileType Excel { get; } = new("Excel")
+    {
+        Patterns = ["*.xlsx"],
+        MimeTypes = ["application/vnd.ms-excel"]
+    };
+}