Categories List component in Oxygen (via the Oxygen WooCommerce integration plugin) outputs all product categories by default.
If you wish to show only the top level i.e., parent product categories go to Categories Query and enter
"0" (including the double quotes) in the Parent field.
where the product categories hierarchy is:
/wp-content/plugins/oxygen-woocommerce/elements/archive-categories.php (around L54)
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