Hello Gianluca,

Thank you for getting in touch with us!

The widget which you would like to use for display a slider is related to the theme developer, so you should contact with them about this issue.

Until then, you can show sliders on your website with other publishing methods, for example shortcode.
Please check this link in our documentation page for some more details:
https://layerslider.kreaturamedia.com/documentation/#publishing-sliders