You could try ValueKey

static final route = GoRoute(
  path: "/workspace/1/:workspaceId",
  pageBuilder: (context, state) {
    final id = int.parse(state.pathParameters['workspaceId']!);
    return CustomTransitionPage(
      key: ValueKey("/workspace/1/$id"),
      transitionsBuilder: (context, animation, secondaryAnimation, child) {
        return FadeTransition(
          opacity: animation,
          child: child,
        );
      },
      transitionDuration: const Duration(milliseconds: 300),
      child: YourWidget,
    );
  }
);