Hi,
These are not user categories but vendor categories. If you have added at least one category, this category field becomes mandatory, and if there is at least one mandatory field, the Complete profile step appears.
Yes, it is possible to hide the field and make it optional, but it will require custom implementation. If customizations are required for your site, please try customizing it using the collection of code snippets Search · user:hivepress · GitHub and other developer resources, or consider hiring someone for custom work https://fvrr.co/32e7LvY