That feature has been deprecated because it doesn’t work well together with role permissions and tends to confuse people. For example, some users incorrectly assume that it’s the best (or only) way to hide menus. In most cases, it’s much better to instead click on a role and un-check the menus you want to hide.
If you really need the “hide” button for some reason, you can re-enable it by clicking the “Settings” link on the menu editor page and checking the box that says ” Enable the “Show/Hide” toolbar button”.
Note: These support forums are mainly intended for the free version of the plugin. For the Pro version, please use this contact form instead.