hm, not sure if adding another dimension of sorting is helpful currently.
tagging, categories etc. always imply a bit that things are sorted to them, which is actually not even true for the “desktop” category. also wondering how this looks like - i have not seen tags in some discourse forum yet - or i’ve overseen them
but what about adding the subcategories “android”, “desktop”, “ios” for both, “mututal help” and “feature requests”? iiuc, the default view of categories is not changed - and when filing a topic you still have to deal with on criterion only - and you can be unspecific. this is what signalusers did.
another option is to just delete the desktop-category and see how this works out - most posts related to desktop are not even in there and also, no one has missed an android category afaik
and we can decide if really need subcategories or tags later.