Hi,
1) I am able to create a new category. I am NOT able to add any category to the Main Menu.
2) Since the link you sent does not work for me to upload anything there here are the EXACT STEPS step by step on seeing what the issue is:
When you go to Dashboard> WooCommerce> Products> Product Data > Select “External/Affiliate Product”> General> Button Text (next to it is a box I have filled in “Buy Product”) and next to that says “This text will be shown on the button linking to the external product”…… THE PROBLEM IS THE BUTTON TEXT DOES NOT APPEAR ON THE PRODUCT LISTING PAGE. THE BUTTON TEXT IS NOT WORKING AND DOES NOT APPEAR.
This is very clear on a step by step instruction on where to find the issue and what the issue is. Hope this helps 🙂