You can't get a horizontal menu to wrap. What you need to do is create a multi-level menu (see the Multi-Level template). The multi-level effect is achieved by enabling the multi-column setting under Popup Menu - Multi-Column
for the Top-level Menu. It may help to load the Multi-Level template and select the Top-level Menu. You will see that under Popup Menu - Multi-Column
the Enable multi-column setting
is checked and the menu uses two rows displayed vertically.
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