Thank you for posting here in the Community, @passuello. I'd like to help you get the option back on the product and services page.

Your account may be using the sub-items feature. We can switch it to Categories by following the steps below. Note: Once modified, you can no longer go back to the sub-items feature.

1. Go to the Gear > Products and Services.
2. In the suggestion box that says Categories make organizing your products and services even easier than sub-items - and can make entering transactions a snap, select the Ready to make your life easier link 
3. Click the Switch now button.

Once done, you can now see the Manage Categories under the More drop-down menu.

Also, you can follow the workaround shared by my colleague to log in to your account as the master admin and open it through a private browser. This is to verify that is not a browser-related issue.

If the issue persists, I highly suggest reaching out to our technical support team. They can securely do a remote session with you to help check and identify the cause and fix the problem. Just click this link on how to reach them: Customer Care Team.

I'll add this article as your reference in grouping items when managing categories: 

• Group your product and services into different categories
• Change The Account for a Product/Service Item.

Please keep in touch with me here should you need any further assistance. I'd be delighted to help you some more. Take care and have a great day, @passuello.