Hi there,
> For this moment, we use Load Group Attributes Product but the plugin is not any more released since three years.
It looks like that plugin page also includes a link to where you could purchase a version of the plugin that may be more up to date: https://www.zhaket.com/web/fast-attributes-woocommerce-plugin
> We bought WooCommerce Group Attributes but when install it, we see that the front-end design of the list of attributes is changed, so that its impossible to read correctly the attributes.
I recommend reaching out to their support as they may be able to help you troubleshoot/customize the functionality you’re looking for for your site:
https://www.welaunch.io/en/contact/#new-ticket
> Have you any idea of a serious plugin who can help us ?
Are you looking to add default attributes to the front end? If so, there are a few ways to add this functionality to your site. I recommend checking out tutorials like this one:
https://quadlayers.com/default-product-attributes-woocommerce/
Or are you wanting to add default attributes to the edit product page? If you are technically minded, this custom code may also help:
https://gist.github.com/Jon007/ae3a112659d6670ebbd2f26d55143773
Customizations can be done via a functionality plugin (https://css-tricks.com/wordpress-functionality-plugins/). This is a simple plugin that contains anything you would otherwise paste in functions.php and it is advantageous because it’s theme-independent.
If the available solutions are not giving you the functionality you’re looking for or if it’s outside of your comfort zone, you may also want to look into hiring a developer. In that case, we can recommend contacting one of the services on our WooCommerce Customizations Page.