Just had a look at v7 it is under Collections there, so have a look there. I only use 6.10.8 and have 7.0 as test site.
EDIT1 :: Just installing 6.11
EDIT2 :: Yeap! under Collections in 6.11 :)

Yeap! under Collections in 6.11 :)

You mean Collection Menue Item in top line as shown below? i seem to have a reduced menue anyways, don't I ?

Not the back office?? It's a front office option to show the containers and widgets for each collection.

The reduced menu in the back office is correct.

Thanks for checking again. Meanwhile I found out myself: it is only in front office menue.
Means: Users can switch container show/hide only in front-office.
This seems strange. Why should the back office level allow less menue-options than the front office .. and also: isn't it rather admins who needed exactly this feature

You need to see the whole user screen to manage the containers so you need the front office and users can't see the option without permission.(admin etc.)

There are no containers to show or hide when you are in the backoffice.