Composer update ended up saying Trait 'Carbon\Traits\Mixin' not found

I installed a new XAMPP with a higher version of PHP (7.2.21) on my windows machine and moved my Laravel project there. When I ran composer update in my project root everything went well but at the end it gave the following:

Generating optimized autoload files
> Illuminate\Foundation\ComposerScripts::postAutoloadDump
> @php artisan package:discover --ansi

In Macro.php line 33:

  Trait 'Carbon\Traits\Mixin' not found


PHP Fatal error:  Trait 'Carbon\Traits\Mixin' not found in D:\xampp\htdocs\myproject\vendor\nesbot\carbon\src\Carbon\Traits\Macro.php on line 33
Script @php artisan package:discover --ansi handling the post-autoload-dump event returned with error code 255

I googled the error but found really nothing about this. What am I missing?

via Chebli Mohamed