Dont show disabled modules in "Disable Modules Output" config

app/code/core/Mage/Adminhtml/Block/System/Config/Form/Fieldset/Modules/DisableOutput.php

@@ -27,17 +27,7 @@ public function render(Varien_Data_Form_Element_Abstract $element)
     {
         $html = $this->_getHeaderHtml($element);
 
-        $modules = array_keys((array)Mage::getConfig()->getNode('modules')->children());
-
-        $dispatchResult = new Varien_Object($modules);
-        Mage::dispatchEvent(
-            'adminhtml_system_config_advanced_disableoutput_render_before',
-            ['modules' => $dispatchResult]
-        );
-        $modules = $dispatchResult->toArray();
-
-        sort($modules);
-
+        $modules = $this->getModules();
         foreach ($modules as $moduleName) {
             if ($moduleName === 'Mage_Adminhtml') {
                 continue;
@@ -49,6 +39,22 @@ public function render(Varien_Data_Form_Element_Abstract $element)
         return $html;
     }
 
+    public function getModules(): array
+    {
+        $modules = (array)Mage::getConfig()->getNode('modules')->children();
+
+        $dispatchResult = new Varien_Object($modules);
+        Mage::dispatchEvent(
+            'adminhtml_system_config_advanced_disableoutput_render_before',
+            ['modules' => $dispatchResult]
+        );
+        $modules = array_keys($dispatchResult->toArray());
+
+        sort($modules);
+
+        return $modules;
+    }
+
     protected function _getDummyElement()
     {
         if (empty($this->_dummyElement)) {

app/code/core/Mage/Adminhtml/Model/System/Config/Backend/Admin/Observer.php

@@ -44,4 +44,24 @@ public function afterCustomUrlChanged($observer)
             ->sendResponse();
         exit(0);
     }
+
+    /**
+     * Hide disabled modules
+     *
+     * @see Mage_Adminhtml_Block_System_Config_Form_Fieldset_Modules_DisableOutput::render()
+     */
+    public function beforeRenderModuleList(Varien_Event_Observer $observer): void
+    {
+        $event = $observer->getDataByKey('event');
+        $modules = $event->getDataByKey('modules');
+        $data = $modules->getData();
+        /** @var Mage_Core_Model_Config_Element $module */
+        foreach ($data as $index => $module) {
+            $module = $module->asArray();
+            if ($module['active'] === 'false') {
+                unset($data[$index]);
+            }
+        }
+        $modules->setData($data);
+    }
 }

app/code/core/Mage/Adminhtml/etc/config.xml

@@ -115,6 +115,14 @@
                     </bind_locale>
                 </observers>
             </admin_system_config_changed_section_admin>
+            <adminhtml_system_config_advanced_disableoutput_render_before>
+                <observers>
+                    <hide_disabled>
+                        <class>adminhtml/system_config_backend_admin_observer</class>
+                        <method>beforeRenderModuleList</method>
+                    </hide_disabled>
+                </observers>
+            </adminhtml_system_config_advanced_disableoutput_render_before>
         </events>
         <global_search>
             <products>

tests/unit/Mage/Adminhtml/Block/System/Config/Form/Fieldset/Modules/DisableOutputTest.php

@@ -0,0 +1,65 @@
+<?php
+
+/**
+ * OpenMage
+ *
+ * This source file is subject to the Open Software License (OSL 3.0)
+ * that is bundled with this package in the file LICENSE.txt.
+ * It is also available at https://opensource.org/license/osl-3-0-php
+ *
+ * @category   OpenMage
+ * @package    OpenMage_Tests
+ * @copyright  Copyright (c) 2024 The OpenMage Contributors (https://www.openmage.org)
+ * @license    https://opensource.org/licenses/osl-3.0.php  Open Software License (OSL 3.0)
+ */
+
+declare(strict_types=1);
+
+namespace OpenMage\Tests\Unit\Mage\Adminhtml\Block\System\Config\Form\Fieldset\Modules;
+
+use Generator;
+use Mage;
+use Mage_Adminhtml_Block_System_Config_Form_Fieldset_Modules_DisableOutput;
+use PHPUnit\Framework\TestCase;
+
+class DisableOutputTest extends TestCase
+{
+    public Mage_Adminhtml_Block_System_Config_Form_Fieldset_Modules_DisableOutput $subject;
+
+    public function setUp(): void
+    {
+        Mage::app();
+        // phpcs:ignore Ecg.Classes.ObjectInstantiation.DirectInstantiation
+        $this->subject = new Mage_Adminhtml_Block_System_Config_Form_Fieldset_Modules_DisableOutput();
+    }
+
+    /**
+     * @group Mage_Adminhtml
+     * @group Mage_Adminhtml_Block
+     */
+    public function testGetModulesCount(): void
+    {
+        $this->assertSame(61, count($this->subject->getModules()));
+    }
+
+    /**
+     * @dataProvider provideModules
+     * @group Mage_Adminhtml
+     * @group Mage_Adminhtml_Block
+     */
+    public function testGetModules(string $module): void
+    {
+        $result = $this->subject->getModules();
+        $this->assertArrayHasKey($module, array_flip($result));
+    }
+
+    public function provideModules(): Generator
+    {
+        yield 'Mage_Admin' => [
+          'Mage_Admin'
+        ];
+        yield 'Mage_Core' => [
+          'Mage_Core'
+        ];
+    }
+}