If I haven't had a full or part time job in 2021; however, I sold some items on Amazon.com. In this case, what should I answer for: did you work in 2021?

You would answer "Yes" that you worked.  Also that you were self-employed.

as per CRA: When you sell on a platform this is what you must do.

 As per QuickBooks: As a resident of Canada, you are responsible for reporting any income you earn from Amazon to the CRA. For tax purposes, you are considered a small business and need to submit Form T2125 with your tax return. You must report Canadian earnings as well as money you earned from American buyers and should convert all transactions into Canadian dollars. If you register as a professional seller with Amazon or handle more than 50 transactions per year, you also have to submit Form W-8BEN to Amazon so it may pass the information to the Internal Revenue Service in the United States.

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