Hello

Thank you for your query.

Please add the following css rule in custom css section. This will hide the main menu below 1200px and show the offcanvas menu

@media (max-width: 1199px) {
    .sp-megamenu-parent {
        display: none;
    }
    #offcanvas-toggler {
        display: block !important;
    }
}

Thank you ! i add this but nothing seem happen, when i reseize the width it follow the old behavior !

Could you kindly share your admin access? Use the hidden mode to share the log in credentials, please.