Use wp_get_nav_menu_items
to get the items from your menu.
Use wp_list_pluck
to extract just the object_id
from each menu item. This is the ID of the page the menu item refers to.
You’ll now have an array of the page IDs in the order they appear in the menu.
Create a new WP_Query
for post_type
page
and pass that array as post__in
argument, and set orderby
to post__in
.