diff --git a/wp-admin/includes/class-wp-list-table.php b/wp-admin/includes/class-wp-list-table.php
index b8631d17a2..c7c38a3561 100644
--- a/wp-admin/includes/class-wp-list-table.php
+++ b/wp-admin/includes/class-wp-list-table.php
@@ -176,6 +176,7 @@ class WP_List_Table {
 	 * Makes private properties readable for backward compatibility.
 	 *
 	 * @since 4.0.0
+	 * @since 6.4.0 Getting a dynamic property is deprecated.
 	 *
 	 * @param string $name Property to get.
 	 * @return mixed Property.
@@ -184,27 +185,42 @@ class WP_List_Table {
 		if ( in_array( $name, $this->compat_fields, true ) ) {
 			return $this->$name;
 		}
+
+		trigger_error(
+			"The property `{$name}` is not defined. Getting a dynamic (undefined) property is " .
+			'deprecated since version 6.4.0! Instead, define the property on the class.',
+			E_USER_DEPRECATED
+		);
+		return null;
 	}
 
 	/**
 	 * Makes private properties settable for backward compatibility.
 	 *
 	 * @since 4.0.0
+	 * @since 6.4.0 Setting a dynamic property is deprecated.
 	 *
 	 * @param string $name  Property to check if set.
 	 * @param mixed  $value Property value.
-	 * @return mixed Newly-set property.
 	 */
 	public function __set( $name, $value ) {
 		if ( in_array( $name, $this->compat_fields, true ) ) {
-			return $this->$name = $value;
+			$this->$name = $value;
+			return;
 		}
+
+		trigger_error(
+			"The property `{$name}` is not defined. Setting a dynamic (undefined) property is " .
+			'deprecated since version 6.4.0! Instead, define the property on the class.',
+			E_USER_DEPRECATED
+		);
 	}
 
 	/**
 	 * Makes private properties checkable for backward compatibility.
 	 *
 	 * @since 4.0.0
+	 * @since 6.4.0 Checking a dynamic property is deprecated.
 	 *
 	 * @param string $name Property to check if set.
 	 * @return bool Whether the property is a back-compat property and it is set.
@@ -214,6 +230,11 @@ class WP_List_Table {
 			return isset( $this->$name );
 		}
 
+		trigger_error(
+			"The property `{$name}` is not defined. Checking `isset()` on a dynamic (undefined) property " .
+			'is deprecated since version 6.4.0! Instead, define the property on the class.',
+			E_USER_DEPRECATED
+		);
 		return false;
 	}
 
@@ -221,13 +242,21 @@ class WP_List_Table {
 	 * Makes private properties un-settable for backward compatibility.
 	 *
 	 * @since 4.0.0
+	 * @since 6.4.0 Unsetting a dynamic property is deprecated.
 	 *
 	 * @param string $name Property to unset.
 	 */
 	public function __unset( $name ) {
 		if ( in_array( $name, $this->compat_fields, true ) ) {
 			unset( $this->$name );
+			return;
 		}
+
+		trigger_error(
+			"A property `{$name}` is not defined. Unsetting a dynamic (undefined) property is " .
+			'deprecated since version 6.4.0! Instead, define the property on the class.',
+			E_USER_DEPRECATED
+		);
 	}
 
 	/**
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 15c01c77e6..faf79696a8 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.4-alpha-56348';
+$wp_version = '6.4-alpha-56349';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.