Currently some categories have 5 or 10 files 📁 and a couple of sub-categories in Wikimedia Commons with a similar amount of files 📁in each sub-categories, while other categories have 0 files (meta-categories) but have sub-categories that can have a few hundred files 📁. Currently there isn't a way to see how much files are in a category if you would count ALL of the files 📁 in its sub-categories, sub-sub-categories, sub-sub-sub-categories, Etc. This would be mostly handy for maintenance ⛑🏻 and for generating accurate statistics regarding certain subjects (for example the total number of images related to a certain human settlement or of a certain subject).
This functionality already exists via https://www.mediawiki.org/wiki/API:Categorymembers (and anyone is free to visualize the results somehow).
For future reference, please structure your tasks into 1) Steps to reproduce including an example link, 2) expected outcome, and 3) actual outcome, plus check for existing project tags to add. See https://mediawiki.org/wiki/How_to_report_a_bug for more information. Thanks!