Hello, @Hannes,
1- Please make sure that you have chosen the categories in the widget settings as you can see in this image: https://postimg.cc/Lg21sZDN
2- Also, please make sure that you have created the category in the Dashboard >> Product >> Category, and then you have assigned the products to the categories you have on your store.
3- If still, your issue is not resolved then please share your site wp-admin URL and access in the private content area of this topic by following the below-given format
WORDPRESS ADMIN URL:
WORDPRESS ADMIN USERNAME:
WORDPRESS ADMIN PASSWORD:
So that I will check your issue on your site and assist you accordingly.
Regards 8Themes Team.