Try adding plugin repository again

Jellyfin.Server/Migrations/MigrationRunner.cs

@@ -21,7 +21,8 @@ namespace Jellyfin.Server.Migrations
             typeof(Routines.MigrateActivityLogDb),
             typeof(Routines.RemoveDuplicateExtras),
             typeof(Routines.AddDefaultPluginRepository),
-            typeof(Routines.MigrateUserDb)
+            typeof(Routines.MigrateUserDb),
+            typeof(Routines.ReaddDefaultPluginRepository)
         };
 
         /// <summary>

Jellyfin.Server/Migrations/Routines/ReaddDefaultPluginRepository.cs

@@ -0,0 +1,49 @@
+using System;
+using MediaBrowser.Controller.Configuration;
+using MediaBrowser.Model.Updates;
+
+namespace Jellyfin.Server.Migrations.Routines
+{
+    /// <summary>
+    /// Migration to initialize system configuration with the default plugin repository.
+    /// </summary>
+    public class ReaddDefaultPluginRepository : IMigrationRoutine
+    {
+        private readonly IServerConfigurationManager _serverConfigurationManager;
+
+        private readonly RepositoryInfo _defaultRepositoryInfo = new RepositoryInfo
+        {
+            Name = "Jellyfin Stable",
+            Url = "https://repo.jellyfin.org/releases/plugin/manifest-stable.json"
+        };
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="ReaddDefaultPluginRepository"/> class.
+        /// </summary>
+        /// <param name="serverConfigurationManager">Instance of the <see cref="IServerConfigurationManager"/> interface.</param>
+        public ReaddDefaultPluginRepository(IServerConfigurationManager serverConfigurationManager)
+        {
+            _serverConfigurationManager = serverConfigurationManager;
+        }
+
+        /// <inheritdoc/>
+        public Guid Id => Guid.Parse("5F86E7F6-D966-4C77-849D-7A7B40B68C4E");
+
+        /// <inheritdoc/>
+        public string Name => "ReaddDefaultPluginRepository";
+
+        /// <inheritdoc/>
+        public bool PerformOnNewInstall => true;
+
+        /// <inheritdoc/>
+        public void Perform()
+        {
+            // Only add if repository list is empty
+            if (_serverConfigurationManager.Configuration.PluginRepositories.Count == 0)
+            {
+                _serverConfigurationManager.Configuration.PluginRepositories.Add(_defaultRepositoryInfo);
+                _serverConfigurationManager.SaveConfiguration();
+            }
+        }
+    }
+}