Hi! If there are many subcategories, the user may find it difficult to search for the desired subcategory. Therefore, it would be nice if user could select the main category first, and then the subcategory, this will make it easier for the user to submit the ad.

@alex7070
Different themes use different category selector design.
There are also different options in osclass directly, check docs or search on forums.

I mean the default Sigma theme. Everything is done correctly in the administration panel, it is easy for the administrator to edit ads ( in the screenshot). Why not make it easy for the user to add and edit ads as well? There are thousands of classifieds sites and if the user sees even a slight inconvenience, he will go to another bulletin board site.