It's a slim possibility but I'll ask anyway. Particularly addressed to Peter, John EB, Walter, and any other German-speaking users in case they have come across anything relevant in the German forum.

To help me with certain macro scripts I want a KB shortcut or other method/hack that will let me quickly close any open ('expanded'?) categories in this pane:

So it would close Video effects, to give this result:

And so on, closing all open categories, without any manual intervention.

Not surprisingly, File > Settings > Keyboard shortcuts has nothing.