Menubar in digiKam
Solution 1:
Try CTRL+M which switches the menu bar on and off.
Solution 2:
I've had to edit in 'MenuBar=Enabled' into that file you mentioned ( ~/.kde/share/config/digikamrc ).
When I next launched Digikam, the menu was there. However, after closing off that session and reopening Digikam at a later date, it was gone again.
Luckily with Ubuntu there's the HUD, so by hitting the left alt key and typing whatever I'm looking for I can so far get access to the features I need. And if I type 'settings', one for 'Show Menubar' re-appears. It's a really puzzling bug for sure.