diff -r 7b1b88e27a20 -r 48c4eec2b7e6 wp/wp-includes/class-wp-widget.php
--- a/wp/wp-includes/class-wp-widget.php	Thu Sep 29 08:06:27 2022 +0200
+++ b/wp/wp-includes/class-wp-widget.php	Fri Sep 05 18:40:08 2025 +0200
@@ -17,6 +17,7 @@
  * @since 2.8.0
  * @since 4.4.0 Moved to its own file from wp-includes/widgets.php
  */
+#[AllowDynamicProperties]
 class WP_Widget {
 
 	/**
@@ -151,7 +152,7 @@
 	 *
 	 * @since 2.8.0
 	 *
-	 * @param string $id_base         Optional. Base ID for the widget, lowercase and unique. If left empty,
+	 * @param string $id_base         Base ID for the widget, lowercase and unique. If left empty,
 	 *                                a portion of the widget's PHP class name will be used. Has to be unique.
 	 * @param string $name            Name for the widget displayed on the configuration page.
 	 * @param array  $widget_options  Optional. Widget options. See wp_register_sidebar_widget() for
@@ -187,7 +188,7 @@
 	 *
 	 * @see WP_Widget::__construct()
 	 *
-	 * @param string $id_base         Optional. Base ID for the widget, lowercase and unique. If left empty,
+	 * @param string $id_base         Base ID for the widget, lowercase and unique. If left empty,
 	 *                                a portion of the widget's PHP class name will be used. Has to be unique.
 	 * @param string $name            Name for the widget displayed on the configuration page.
 	 * @param array  $widget_options  Optional. Widget options. See wp_register_sidebar_widget() for
@@ -428,14 +429,14 @@
 			if ( isset( $wp_registered_widgets[ $del_id ]['params'][0]['number'] ) ) {
 				$number = $wp_registered_widgets[ $del_id ]['params'][0]['number'];
 
-				if ( $this->id_base . '-' . $number == $del_id ) {
+				if ( $this->id_base . '-' . $number === $del_id ) {
 					unset( $all_instances[ $number ] );
 				}
 			}
 		} else {
 			if ( isset( $_POST[ 'widget-' . $this->id_base ] ) && is_array( $_POST[ 'widget-' . $this->id_base ] ) ) {
 				$settings = $_POST[ 'widget-' . $this->id_base ];
-			} elseif ( isset( $_POST['id_base'] ) && $_POST['id_base'] == $this->id_base ) {
+			} elseif ( isset( $_POST['id_base'] ) && $_POST['id_base'] === $this->id_base ) {
 				$num      = $_POST['multi_number'] ? (int) $_POST['multi_number'] : (int) $_POST['widget_number'];
 				$settings = array( $num => array() );
 			} else {
@@ -507,7 +508,7 @@
 		$widget_args   = wp_parse_args( $widget_args, array( 'number' => -1 ) );
 		$all_instances = $this->get_settings();
 
-		if ( -1 == $widget_args['number'] ) {
+		if ( -1 === $widget_args['number'] ) {
 			// We echo out a form where 'number' can be set later.
 			$this->_set( '__i__' );
 			$instance = array();
@@ -612,12 +613,16 @@
 		$settings = get_option( $this->option_name );
 
 		if ( false === $settings ) {
+			$settings = array();
 			if ( isset( $this->alt_option_name ) ) {
-				$settings = get_option( $this->alt_option_name );
-			} else {
-				// Save an option so it can be autoloaded next time.
-				$this->save_settings( array() );
+				// Get settings from alternative (legacy) option.
+				$settings = get_option( $this->alt_option_name, array() );
+
+				// Delete the alternative (legacy) option as the new option will be created using `$this->option_name`.
+				delete_option( $this->alt_option_name );
 			}
+			// Save an option so it can be autoloaded next time.
+			$this->save_settings( $settings );
 		}
 
 		if ( ! is_array( $settings ) && ! ( $settings instanceof ArrayObject || $settings instanceof ArrayIterator ) ) {