Many marketplaces, including OTTO, provide more extensive or different category trees via their APIs. magnalister uses the categories provided by OTTO and offers them via a category search in the product preparation of the plugin.
You can download an up-to-date overview of which categories OTTO Marketplace provides via its API at https://www.otto.market/en/howitworks/assortment-overview.html. To do so, click on "Download product overview".
In the columns "Category" and "Category Group" you will find all permitted (sub-) categories. The final assignment of the categories from this list to the categories displayed in the marketplace frontend is done independently by OTTO after the product upload by magnalister.
In the magnalister product preparation under "Category Search" you can assign your products to the corresponding OTTO category. Find more information in this FAQ.