Could this extension exclude some categories or only lead to some categories?
Topic on Extension talk:ExcludeRandom/Flow
To exclude categories from showing in Special:Random, you just add the category names to the variable, or a prefix that is shared with categories you don't want to show.
The extension only has the functionality to blacklist not whitelist, so you can't only whitelist some categories, you would have to blacklist everything else, which is unlikely to be practical.