How to add a field in the workflow when I want to create a task

Content (please ensure you mask any confidential information):

I am using the workflow functionality to create tasks. However, in the "task details" section, not all the fields appear. For example, I want the task to be created with a custom field that we have created, called "Category". How do I achieve this?

Version (include the version you are using, if applicable):

24D