Magento 2.4 - Build Child Theme parent of theme installed via composer - themes

Question

I need a tip.
I've installed a theme via composer and I need to create a child theme having as parent a theme installed via composer.
path of theme installed via composer: vendor/{vendor}/{theme}/
path of child theme: app/design/frontend/{vendor}/{theme}/
in the child theme folder i've created:
theme.xml
<theme xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Config/etc/theme.xsd">
<title>TitleTheme</title>
<parent>{folder-name-vendor}/{folder-name-theme}</parent>
<media>
<preview_image>media/preview.jpg</preview_image>
</media>
</theme>
Composer.json
{
"name": "{my-vendor-folder}/{my-child-theme}",
"description": "N/A",
"require": {
"php": "~5.5.0|~5.6.0|~7.0.0",
"magento/framework": "100.0.*"
},
"type": "magento2-theme",
"version": "100.0.2",
"license": [
"OSL-3.0",
"AFL-3.0"
],
"autoload": {
"files": [
"registration.php"
]
}
}
registration.php
<?php
/**
* Copyright © 2015 Magento. All rights reserved.
* See COPYING.txt for license details.
*/
\Magento\Framework\Component\ComponentRegistrar::register(
\Magento\Framework\Component\ComponentRegistrar::THEME,
'frontend/{my-vendor-folder}/{my-child-theme}',
__DIR__
);
When I change the theme from the magento backend panel under
Content > Design > Configuration
and then run:
php bin/magento setup:upgrade
php bin/magento setup:static-content:deploy
It does not load me the parent theme I have chosen, but the default magento theme.I don't know what I'm wrong.
Can someone help me?
Thank you ;)