how do i open menus in rtl alignments?

You can use the overlap property to shift the submenu over to the position you want.

Note that if the position of the menu is too close to the left or right edge of the window, it will still open on the opposite side.

Menu {
    id: right_menu
    property var rtl: true;

    MenuItem {
        text: "گزینه ۱"
        LayoutMirroring.enabled: true
        LayoutMirroring.childrenInherit: true
    }

    Menu {
        title: "تنظیمات"
        overlap: width * 2  // <<-- Shift the submenu over

        MenuItem {
            LayoutMirroring.enabled: true
            LayoutMirroring.childrenInherit: true
            text: "گزینه ۱"
        }

        MenuItem {
            LayoutMirroring.enabled: true
            LayoutMirroring.childrenInherit: true
            text: "گزینه ۱"
        }
    }

    delegate: MenuItem {
        LayoutMirroring.enabled: true
        LayoutMirroring.childrenInherit: true
    }
}