How to remove white overlay on Slideshow image?

 You have to use custom CSS to remove white transparent overlay:

.sppb-fullwidth-slider .sppb-fullwidth-slider-item-bg::before { background-image: none;}

Offcanvas menu: missing icon (toggler) to open submenu items

If even after changing the menu items type and correct setting in the menu module you still do not see (+) to open submenu items in the Mobile menu, please use below custom CSS:

.menu-toggler::after {
  content: "\f055";
  font-family: "Font Awesome 5 Free";
  font-weight: bold;
}

.offcanvas-inner .sp-module ul > li span.menu-toggler {
  display: block;
  position: absolute;
  top: 50%;
  right: 0px;
  transform: translateY(-50%);
    cursor: pointer;
}

.offcanvas-menu .offcanvas-inner .sp-module ul > li.menu-parent.menu-parent-open > a > .menu-toggler::after,
.offcanvas-menu .offcanvas-inner .sp-module ul > li.menu-parent.menu-parent-open > .menu-separator > .menu-toggler::after {
  content: "\f056";
}