It seems, kdenlive is not very standard kde app. There is additional switch menu on the right
I have global menu enabled, and it just eats kdenlive menu, without providing anything to the widget.

Can it be fixed? I dont need this right menu, I am happy with default layout.
Or, for the worst scenario - how to exclude kdenlive from global menu interaction?

Are you talking about the menu to change the layouts? See if it helps:

View -> Manage Layouts -> Add or Delete whatever you want but...

It has a bug for me... If I remove all the layouts it will go back to default and bring me back all the fives so I have to keep one, but one is ok for me