Converted to TS, add import

app/Http/Middleware/HandleInertiaRequests.php

@@ -33,6 +33,7 @@ class HandleInertiaRequests extends Middleware
             ...parent::share($request),
             'auth' => [
                 'user' => $request->user(),
+                'isLoggedIn' => $request->user() !== null,
             ],
         ];
     }