Your question is a little bit confusing. There is no field named Optional under the chart of accounts or on any screen. Many data input fields throughout Manager show the word Optional in grey by default. This only means that entering content in that field is optional.
When creating or editing an individual account, the Code field shows Optional by default. This field allows you to enter an account code. See this Guide:
Can you explain further what you mean by this? Accounts do not have “subcategories.” Accounts can be assigned to Groups, however.
The answer, and whether you can do what you want at all, depends on what you want the report to show. As a first step, click on the balance for an account in the Summary. You can export the listing and manipulate the data as desired in a spreadsheet.