Rethinking the header – its visual weight and its navigation purposes

Introduction:
A web site’s navigation menus usually get placed at:
a) the top area of a web page – filling the header, that is;
b) the top (the header), on demand – by means of a hamburger menu button;
c) top + left-hand column;
d) top + f…
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is there a limit of list items displayed on mega menus?

So I’ve redesigning this web that has a lot of menus (> 100 menus total in my app). Is there a limit of list items displayed on mega menus?
and what should be the best behavior for "See More" button on mega menu? I’ve been th…