Default category in Magento 2

[foysal]

How to delete default category in Magento 2 ?

[Manish Mittal]

@foysal

Because Root category is the highest level of category, so you can't remove it while it is active or there is a store assigned to it. Therefore, if you want to delete a root category, you need to check what its status first. Then when you choose the Root category in Admin page, the Delete button will show up.

Follow below link for your reference:

https://www.magestore.com/magento-2-tutorial/add-and-delete-root-category-in-magento-2/

[Shiwani Miglani]

You can delete a root category if no store has been assigned to it. 

Check System then go to Manage Stores