Updated on February 18, 2020
Categories List component in Oxygen (via the Oxygen WooCommerce integration plugin) outputs all product categories by default.
To show only the top-level i.e., parent product categories we used to be able to enter "0" (including the double quotes) in the Parent field for the Categories Query.
Before:
After:
where the product categories hierarchy is:
But this no longer works on the front end as of Oxygen 3.1.1.
This premium members-only tutorial provides two ways to restrict the product categories to top level only.