For one thing I found a reply by myself: categories are not expanding cause I removed the function on Top Menu cause they are too many (but that's not a real problem).
What is very strange is that only on homepage the "menù" button is not clickable. What I also realized when checking for translations is that the button on the homepage is part of "blockcategories" module. When in other pages it's part of "blocktopmenu" so only the first one seems to be not clickable... very strange