错误的代码部分是compact($users)，它必须是compact('users').固定代码为

Wrong part of your code is compact($users) It must be compact('users'). Fixed code is

public function index()
{
    $users = \App\User::all();
    return view('users.index', compact('users');
}

compact('users')是等效的 ['users'=> $ users]