Może ten błąd podczas instalacji coś powie? Ale composera przed tym projektem odinstalowałem i zainstalowałem jeszcze raz.
Reading C:\xampp\htdocs\testowa/composer.json
Loading config file C:\xampp\htdocs\testowa/composer.json
Failed to initialize global composer: Composer could not find the config file: C:/xampp/htdocs/testowa/var/composer_home/composer.json
To initialize a project, please create a composer.json file as described in the https://getcomposer.org/ "Getting Started" section
Reading C:\xampp\htdocs\testowa/vendor/composer/installed.json
Reading C:\xampp\htdocs\testowa/composer.lock
Checking for "magento/composer-root-update-plugin: 1.1.2" for the Web Setup Wizard...
Reading C:\xampp\htdocs\testowa/var/vendor/magento/composer-root-update-plugin/composer.json
Loading config file C:\xampp\htdocs\testowa/var/vendor/magento/composer-root-update-plugin/composer.json
No Web Setup Wizard update needed for magento/composer-root-update-plugin; version 1.1.2 is already in C:\xampp\htdocs\testowa/var.