Installation in backpack... medialibrary 9.3.0, backpack 4.1, laravel 8.12.0

[snipiba]

  Class name must be a valid object or a string

  at \vendor\spatie\laravel-medialibrary\src\MediaLibraryServiceProvider.php:23
     19▕         $this->registerPublishables();
     20▕
     21▕         $mediaClass = config('media-library.media_model');
     22▕
  ➜  23▕         $mediaClass::observe(new MediaObserver());
     24▕
     25▕         $this->loadViewsFrom(__DIR__.'/../resources/views', 'media-library');
     26▕     }
     27▕

  1   \vendor\laravel\framework\src\Illuminate\Container\BoundMethod.php:36
      Spatie\MediaLibrary\MediaLibraryServiceProvider::boot()

  2   \vendor\laravel\framework\src\Illuminate\Container\Util.php:40
      Illuminate\Container\BoundMethod::Illuminate\Container\{closure}()
Script @php artisan package:discover --ansi handling the post-autoload-dump event returned with error code 1

Installation failed, reverting ./composer.json and ./composer.lock to their original content.

env.:

PHP 7.4.2, Laravel 8.12.0, Backpack 4.1
Required installation of medialibrary 9.3.0

Updating dependencies
Lock file operations: 7 installs, 0 updates, 0 removals
  - Locking league/glide (1.7.0)
  - Locking maennchen/zipstream-php (2.1.0)
  - Locking myclabs/php-enum (1.7.7)
  - Locking spatie/image (1.10.0)
  - Locking spatie/image-optimizer (1.3.2)
  - Locking spatie/laravel-medialibrary (9.3.0)
  - Locking spatie/temporary-directory (1.3.0)
Writing lock file
Installing dependencies from lock file (including require-dev)
Package operations: 0 installs, 1 update, 0 removals
  - Downloading spatie/laravel-medialibrary (9.3.0)
  - Upgrading spatie/laravel-medialibrary (9.0.0 => 9.3.0): Extracting archive
3 package suggestions were added by new dependencies, use `composer suggest` to see details.

Failed at postAutoloadDump

[snipiba]

Update, when removed part from "post-autoload-dump": where is requested package discovering, installation was ok. But.. it will be good, when this default laravel composer.json will work at all