laravel 8 Target class [FormController] does not exist. code example

Example 1: Target class [SallyController] does not exist.

//In laravel 8 uncomment  protected $namespace='App\\Http\\Controllers';

Example 2: laravel 8 Target class [FormController] does not exist.

use App\Http\Controllers\UserController;

Route::get('/users', [UserController::class, 'index']);
// or
Route::get('/users', 'App\Http\Controllers\UserController@index');