Thread:Project:Support desk/Find talk pages by the categorization of it's associated content NS?

I'm trying to hack Special:RecentChanges with $wgAllowCategorizedRecentChanges = true.

As stated in T85745, using the "associated namespace" option does not find Talk:Foo (uncategorized) when searching for categories of Foo.

I want to fix this but before I try my usual trial & error struggle with MySQL: Is there a standard function for this already?