Thanks for bringing this concern to my attention, Matteo. Let me share an information about importing product categories and subcategories using CSV file.
Importing categories using CSV file is currently available on the BETA interface in QuickBooks and to some customers. However, if you have the old version when you create the new company account, you can't switch it to the new one and vice versa.
You can view the screenshot below for the BETA and old Products & Services interfaces for comparison:

Moreover, since you can't add a category column while importing your file, you can add the categories and subcategories in the Product name. However, you can't view them when you run a report about your product.
Please refer to the screenshot below for the format:

Additionally, you can use a report to see your sales and inventory status in QuickBooks. You may also run other financial reports and customize them according to your preferences.
Keep me posted if you have other questions about importing categories using CSV file or any other QuickBooks-related concerns. I'll be here to provide you with the assistance you'll need.