Getting custom icons to work via gresource

[PlatinumLucario]

I'm currently experimenting around with custom icons. And to achieve this, I've been looking into Denaro's code and tried implementing the same result.

Unfortunately though, the custom icons I made doesn't work in the test application I've developed on Ubuntu that I've been experimenting around with. As seen here:

So I'm really curious as to what I'm missing? I really thought I implemented everything that I could see from Denaro's code.

Test Project.csproj

<Project Sdk="Microsoft.NET.Sdk">

	<PropertyGroup>
		<OutputType>Exe</OutputType>
		<TargetFramework>net8.0</TargetFramework>
		<Nullable>enable</Nullable>
		<AllowUnsafeBlocks>true</AllowUnsafeBlocks>
	</PropertyGroup>

	<ItemGroup>
		<PackageReference Include="GirCore.Adw-1" Version="0.5.0" />
	</ItemGroup>

	<Target Name="PreBuild" BeforeTargets="PreBuildEvent">
		<Exec Command="glib-compile-resources --sourcedir ./Properties ./Properties/org.resource.test.gresource.xml --target=$(OutDir)/org.resource.test.gresource" />
	</Target>

</Project>

Program.cs

using Adw;
using System;
using System.Runtime.InteropServices;
using System.Collections.Generic;
using System.Globalization;
using System.IO;
using System.Reflection;

namespace Kermalis.VGMusicStudio.GTK4
{
	class Program
	{
		public Program()
		{
		}

		static void OnActivate(object sender, EventArgs e)
		{
			var win = new TestWindow();
			win.SetApplication((Gtk.Application)sender);

			win.Present();
			win.Unref();
		}

		static void OnOpen(Gio.Application sender, Gio.Application.OpenSignalArgs args)
		{
			OnActivate(sender, args);
		}

		static int Main(string[] args)
		{
			var app = Adw.Application.New("org.resource.test", Gio.ApplicationFlags.FlagsNone);
			app.Register(Gio.Cancellable.GetCurrent());
			GLib.Functions.Setenv("GSK_RENDERER", "cairo", false);
			app.OnActivate += OnActivate;
			if (File.Exists(Path.GetFullPath(Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location)!) + "/org.resource.test.gresource"))
			{
				//Load file from program directory, required for `dotnet run`
				Gio.Functions.ResourcesRegister(Gio.Functions.ResourceLoad(Path.GetFullPath(Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location)!) + "/org.resource.test.gresource"));
			}
			else
			{
				var prefixes = new List<string> {
					Directory.GetParent(Directory.GetParent(Path.GetFullPath(Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location)!))!.FullName)!.FullName,
					Directory.GetParent(Path.GetFullPath(Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location)!))!.FullName,
					"/usr"
				};
				foreach (var prefix in prefixes)
				{
					if (File.Exists(prefix + "/share/org.resource.test/org.resource.test.gresource"))
					{
						Gio.Functions.ResourcesRegister(Gio.Functions.ResourceLoad(Path.GetFullPath(prefix + "/share/org.resource.test/org.resource.test.gresource")));
						break;
					}
				}
			}
			app.OnOpen += OnOpen;
			var stat = app.Run(args.Length, args);
			app.Unref();
			return stat;
		}
	}
}

TestWindow.cs

public class TestWindow : Gtk.Window
{
    public TestWindow()
    {
        Title = "Test Window";
        DefaultWidth = 200;
        DefaultHeight = 200;
        Child = Gtk.Image.NewFromIconName("vgms-playlist-symbolic");
    }
}

org.resource.test/gresource.xml

<?xml version="1.0" encoding="UTF-8"?>
<gresources>
  <gresource prefix="/org/resource/test/icons/scalable/playlist">
    <file preprocess="xml-stripblanks">vgms-song-symbolic.svg</file>
    <file preprocess="xml-stripblanks">vgms-playlist-symbolic.svg</file>
  </gresource>
</gresources>

Now surely I've got the GResource XML in the correct format, right? Because I attempted it in the same format as Denaro. But why isn't the icons working?

If anyone would like to look into the full repo, here it is:
Custom Resource Test.zip

Thank you so much!