is it normal, that there are not many options to configure groupjive?
Yes, GJ 3.x was simplified with template based parameters being removed as they can be adjusted with a custom template.
For example, how many categories or groups are shown in a line, how long the category name can be and will be shown??
Yes, those are all removed. There are pagination parameters though if you're meaning to control how many groups are displayed per page.
And, isn't there a user panel anymore ??
Correct, there is no longer a panel. The Groups tab now shows all the groups relevant to the user as a single display (owned or joined) in addition to a menu item that can show both, joined, invited to, or created.
And, isn't it possible to create sub categories ??
Nesting has been removed for performance reasons. Statistically the functionality was rarely used, but its existence resulted in a massive 80% performance loss. Now GJ handles all category and group access directly in its fast and optimized query with no PHP side conditioning for optimal performance. Before you could only have about 10,000 groups before GJ slowed to a crawl or crashed.