As shown in the following figure:
I can’t find where to configure the functionality of the directory navigation pane
As shown in the following figure:
I don’t really get question - do you look for “file picker” menu? If yes it is not the way how such office integration is expected to work. Integrated CODE/COOL opens a documents from Nextcloud Files using specially crafted URL… there is no way to open files from Collabora menu…
Update: ticking “sidebar” opens another toolbar on the right with more detailed fonts settings
or are you maybe confusing with the feature in Text to show the navigation pane? In Text this is hidden under the button “H1” but that’s a different app