diff --git a/typo3/sysext/core/Classes/Core/Bootstrap.php b/typo3/sysext/core/Classes/Core/Bootstrap.php
index 5b05d04a70cd0061f80244f7483825efe48467b7..a8804d3bbd40bd65ded4a7404f9992da849c87ff 100644
--- a/typo3/sysext/core/Classes/Core/Bootstrap.php
+++ b/typo3/sysext/core/Classes/Core/Bootstrap.php
@@ -257,6 +257,7 @@ class Bootstrap
     {
         $packages = $GLOBALS['TYPO3_CONF_VARS']['EXT']['runtimeActivatedPackages'] ?? [];
         if (!empty($packages)) {
+            trigger_error('Support for runtime activated packages will be removed in TYPO3 v11.0.', E_USER_DEPRECATED);
             foreach ($packages as $runtimeAddedPackageKey) {
                 $packageManager->activatePackageDuringRuntime($runtimeAddedPackageKey);
             }
diff --git a/typo3/sysext/core/Classes/Package/PackageManager.php b/typo3/sysext/core/Classes/Package/PackageManager.php
index 72c0fdb665a115231cb8ac428348a5888557234b..bbfc1d9c7c7b2824794dc733849921e1b2ff623c 100644
--- a/typo3/sysext/core/Classes/Package/PackageManager.php
+++ b/typo3/sysext/core/Classes/Package/PackageManager.php
@@ -317,6 +317,7 @@ class PackageManager implements SingletonInterface
      *
      * @param string $packageKey
      * @return PackageInterface
+     * @deprecated will be removed in TYPO3 v11.0
      */
     protected function registerPackageDuringRuntime($packageKey)
     {
@@ -576,6 +577,7 @@ class PackageManager implements SingletonInterface
      * Enables packages during runtime, but no class aliases will be available
      *
      * @param string $packageKey
+     * @deprecated will be removed in TYPO3 v11.0
      */
     public function activatePackageDuringRuntime($packageKey)
     {
diff --git a/typo3/sysext/core/Documentation/Changelog/master/Deprecation-91030-Runtime-ActivatedPackages.rst b/typo3/sysext/core/Documentation/Changelog/master/Deprecation-91030-Runtime-ActivatedPackages.rst
new file mode 100644
index 0000000000000000000000000000000000000000..7eaf2428af563f20f16b777c5f8bd0823c7c6840
--- /dev/null
+++ b/typo3/sysext/core/Documentation/Changelog/master/Deprecation-91030-Runtime-ActivatedPackages.rst
@@ -0,0 +1,47 @@
+.. include:: ../../Includes.txt
+
+================================================
+Deprecation: #91030 - Runtime-Activated Packages
+================================================
+
+See :issue:`91030`
+
+Description
+===========
+
+TYPO3's global configuration option :php:`$GLOBALS['TYPO3_CONF_VARS']['EXT']['runtimeActivatedPackages']` has been deprecated.
+
+The option to register packages during runtime was introduced as
+a work-around to dynamically modify the "extension list" when migrating from TYPO3 v4.5 to TYPO3 v6.x.
+
+However, using this feature has certain limitations:
+
+* Runtime-activated Extensions cannot add their DI configuration
+* Runtime-activated Extensions make every (!) single TYPO3 request much slower just like back in 6.2.0 times
+
+The main usecase we know from people was to this functionality to enable e.g. extensions such as "devlog", "mask"/"mask_export" or "extensionbuilder" only on development systems.
+
+
+Impact
+======
+
+Having a TYPO3 system using Runtime Activated Packages functionality
+will trigger a PHP deprecation warning on every TYPO3 request.
+
+
+Affected Installations
+======================
+
+TYPO3 installations having the affected option set in either :php:`typo3conf/LocalConfiguration.php` or :php:`typo3conf/AdditionalConfiguration.php`.
+
+
+Migration
+=========
+
+It is recommended - if this functionality is needed - to use TYPO3
+Console and Composer Mode (with require-dev) to achieve a similar behavior.
+
+If it is critical to have such features, consider modifying the extension in question to deal with TYPO3's Context
+feature to enable / disable functionality for Production environment.
+
+.. index:: LocalConfiguration, FullyScanned, ext:core
\ No newline at end of file
diff --git a/typo3/sysext/install/Configuration/ExtensionScanner/Php/ArrayDimensionMatcher.php b/typo3/sysext/install/Configuration/ExtensionScanner/Php/ArrayDimensionMatcher.php
index e251614254c7383fd712b25e96e23d23b21bdd4a..5a847da9235af6775039f0082284303ebd9a2d11 100644
--- a/typo3/sysext/install/Configuration/ExtensionScanner/Php/ArrayDimensionMatcher.php
+++ b/typo3/sysext/install/Configuration/ExtensionScanner/Php/ArrayDimensionMatcher.php
@@ -417,4 +417,9 @@ return [
             'Deprecation-91012-VariousHooksRelatedToTypoScriptFrontendController.rst',
         ],
     ],
+    '$GLOBALS[\'TYPO3_CONF_VARS\'][\'EXT\'][\'runtimeActivatedPackages\']' => [
+        'restFiles' => [
+            'Deprecation-91030-Runtime-ActivatedPackages.rst',
+        ],
+    ],
 ];