Some further digging, the .json of the header does contain the code for a menu.
Somehow, this isn’t used/imported.
"elements": [
{
"id": "14b99eca",
"settings": {
"menu": "header_menu",
"navmenu_align": "right",
"submenu_icon": "classic",
"submenu_animation": "slide_up",
"padding_vertical_menu_item": {
"unit": "px",
"size": 10,
"sizes": []
},
"padding": {
"unit": "px",
"top": "10",
"right": "10",
"bottom": "10",
"left": "10",
"isLinked": true
},
"_margin": {
"unit": "px",
"top": "0",
"right": "0",
"bottom": "0",
"left": "0",
"isLinked": false
},
"_padding": {
"unit": "px",
"top": "0",
"right": "0",
"bottom": "0",
"left": "0",
"isLinked": false
},
"menu_typography_typography": "custom",
"menu_typography_font_size": {
"unit": "px",
"size": 16,
"sizes": []
},
"menu_typography_font_weight": "700",
"color_dropdown_item": "#000000",
"color_dropdown_item_hover": "#1A73E8",
"dropdown_typography_typography": "custom",
"dropdown_typography_font_size": {
"unit": "px",
"size": 14,
"sizes": []
},
"padding_horizontal_dropdown_item": {
"unit": "px",
"size": 20,
"sizes": []
},
"color_menu_item": "#000000",
"color_menu_item_hover": "#1A73E8",
"color_menu_item_active": "#1A73E8",
"color_dropdown_item_active": "#1A73E8",
"dropdown_box_shadow_box_shadow_type": "yes",
"dropdown_box_shadow_box_shadow": {
"horizontal": 0,
"vertical": 10,
"blur": 20,
"spread": 0,
"color": "rgba(0,0,0,0.5)"
},
"divider_border_color": "rgba(196, 196, 196, 0.55)",
"resp_align": "right"
},
"elements": [],
"isInner": false,
"widgetType": "navigation-menu",
"elType": "widget"
}
],
"isInner": false,
"elType": "column"
},