Hello, jchen8.
Thank you for your effort in raising your concern here in the forum. I just want to clarify on what column of Category you're looking for or you want to add?
If you mean account category, you can find it in the accounts column in the credit card account register. The Category field for transactions should automatically show in the register and helps you track expense.
If transactions have been categorized properly when entered, the corresponding category shows in the category column. Attached is a screenshot for your reference:

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