diff --git a/.upgradenotes/MDL-78375-2025021311242423.yml b/.upgradenotes/MDL-78375-2025021311242423.yml
new file mode 100644
index 00000000000..7305738ecdb
--- /dev/null
+++ b/.upgradenotes/MDL-78375-2025021311242423.yml
@@ -0,0 +1,9 @@
+issueNumber: MDL-78375
+notes:
+  core:
+    - message: >
+        Final deprecation of device related theme methods. The following two methods have been
+        removed from the core_useragent class:
+          - core_useragent::get_device_type_theme
+          - core_useragent::get_device_type_cfg_var_name
+      type: removed
diff --git a/lib/classes/useragent.php b/lib/classes/useragent.php
index 1e8cc91ec14..97a8861f052 100644
--- a/lib/classes/useragent.php
+++ b/lib/classes/useragent.php
@@ -230,49 +230,31 @@ class core_useragent {
     }
 
     /**
-     * Returns the theme to use for the given device type.
-     *
-     * This used to be get_selected_theme_for_device_type.
-     * @param null|string $devicetype The device type to find out for. Defaults to the device the user is using,
      * @deprecated since 4.3.
-     * @return bool
      */
+    #[\core\attribute\deprecated(
+        null,
+        since: '4.3',
+        reason: 'All functions associated with device specific themes are being removed',
+        mdl: 'MDL-77793',
+        final: true
+    )]
     public static function get_device_type_theme($devicetype = null) {
-        debugging(
-            __FUNCTION__ . '() is deprecated.' .
-                'All functions associated with device specific themes are being removed.',
-            DEBUG_DEVELOPER
-        );
-        global $CFG;
-        if ($devicetype === null) {
-            $devicetype = self::get_device_type();
-        }
-        $themevarname = self::get_device_type_cfg_var_name($devicetype);
-        if (empty($CFG->$themevarname)) {
-            return false;
-        }
-        return $CFG->$themevarname;
+        \core\deprecation::emit_deprecation_if_present([self::class, __FUNCTION__]);
     }
 
     /**
-     * Returns the CFG var used to find the theme to use for the given device.
-     *
-     * Used to be get_device_cfg_var_name.
-     *
-     * @param null|string $devicetype The device type to find out for. Defaults to the device the user is using,
      * @deprecated since 4.3.
-     * @return string
      */
+    #[\core\attribute\deprecated(
+        null,
+        since: '4.3',
+        reason: 'All functions associated with device specific themes are being removed',
+        mdl: 'MDL-77793',
+        final: true
+    )]
     public static function get_device_type_cfg_var_name($devicetype = null) {
-        debugging(
-            __FUNCTION__ . '() is deprecated.' .
-                'All functions associated with device specific themes are being removed.',
-            DEBUG_DEVELOPER
-        );
-        if ($devicetype == self::DEVICETYPE_DEFAULT || empty($devicetype)) {
-            return 'theme';
-        }
-        return 'theme' . $devicetype;
+        \core\deprecation::emit_deprecation_if_present([self::class, __FUNCTION__]);
     }
 
     /**
diff --git a/lib/deprecatedlib.php b/lib/deprecatedlib.php
index 9ced39fa000..00408da725e 100644
--- a/lib/deprecatedlib.php
+++ b/lib/deprecatedlib.php
@@ -314,6 +314,7 @@ function badges_get_oauth2_service_options() {
  * @deprecated since 4.3.
  */
 #[\core\attribute\deprecated(
+    null,
     since: '4.3',
     reason: 'All functions associated with device specific themes are being removed',
     mdl: 'MDL-77793',
@@ -327,6 +328,7 @@ function theme_is_device_locked() {
  * @deprecated since 4.3.
  */
 #[\core\attribute\deprecated(
+    null,
     since: '4.3',
     reason: 'All functions associated with device specific themes are being removed',
     mdl: 'MDL-77793',