How to fix top naviagation top menu not showing in Magento 2

The most common issue with the main menu is its product categories not showing on the frontend after they were added in the admin panel. The best solution to this is to add new and specify the root category and make all product categories its sub-categories.

Step 1: Add new root category

1. From the Admin sidebar, choose Product > Categories.
2. Click Add Root Category.
3. On the General Information tab:
   • Name your Root Category (root-Site name) in the Name box.
   • Maka sure the Is Active box is changed into Yes.
   • Make sure the Include in Navigation Menu is changed into Yes.
4. Click Save Category.

Step 2: Add a subcategory of the new root category

1. Select the newly created Category.
2. With the new Root Category, click Add SubCategory.
3. Make sure the Name is entered in the Name box; Is Active is change into Yes and Included on the Nav Menu is changed into Yes.
4. Click Save Category.

Step 3: Choose the new Root Category

1. From the Admin side bar, navigate to Stores > All Stores.
2. Click on the Main Menu Store link on the second column and explore the content.
3. In the section of Root Category, click to drop down the list of all Category and choose the new Root Category created earlier (root- Sitename).
4. Click Save Store

New categories you have just created should appear on the Navigation menu now. If it’s not working, make sure you refresh all cache.

php bin/magento cache:clear
php bin/magento cache:flush