What megamenu plugin are you using?
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No ı solve this problem on my own. There a re a settings in appearence>Menus>max mega menu of a menu item >settings
You must enter all menu items then disable arrow.
As you use a commercial theme/plugin and need support, please use their official support channel. We feel they are best equipped to support their products.
https://www.megamenu.com/support/
Commercial products are not supported in these forums. .