Hi there,
I was trying to edit product category, but it only shows classic editor.
Not sure why that occurs. Gutenberg is the default editor newer WordPress versions use. It comes preinstalled.
If your WordPress is updates to the new version but it still uses the classic editor when you edit pages, you may have a plugin installed that forces the site to use classic editor.
This is not something the theme controls, unfortunately. You have to check if plugin list if one exists.
As for customizing woocommerce category pages, You can try this out.
https://www.pootlepress.com/2021/01/how-to-edit-woocommerce-category-pages-no-coding-required/
This should be applicable with GeneratePress as the theme doesn’t interfere with the default features and functions of WordPress.