I'm sorry, the fault is mine. I thought that there should be separate tab for activated Menu Module. But the entrance is by clicking on the title of Module Menu. I found it...
/modules/menus/edit/
Add New Item button is not working
When I changed…
Dear @evgeni
Sorry, I had to describe it in more detail:
I mean, that even activated, I can't see the Module Menu on any tab. I tried with two different CMS installations.
(On the other hand, everything you describe is clear to me.)
Best regards…