Follow the official plugin repository: https://github.com/spatie/laravel-google-calendar (note that the screenshots are a little bit outdated)
Don't do the publish command. The wrapper plugin handles this how it should be done in WinterCMS which is why it is created in the first place. See: https://wintercms.com/docs/v1.2/docs/architecture/using-composer#using-laravel-packages`
composer require aic/wn-googlecalendar-plugin