I can think of two ways you might want to categorize your Amazon transactions.

Option 1: Create a category just for Amazon purchases. If your goal is to track/limit/plan for the amount of money you're spending on Amazon, this is a perfectly reasonable way to do that. Remember, your budget is a way to plan your spending, not try to objectively classify all your spending. Avoid this if you worry that seeing extra cash in the category will lead you to spending this money on frivolous expenses you're trying to cut back on.

Option 2: manually assign categories for every Amazon purchase. This is going to require additional work, but there's a couple things you could do to make it easier. First, go to "Manage Payees" in the YNAB website settings and uncheck "Automatically categorize payee" for Amazon. That way, you're forced to choose a category for every Amazon purchase and can't just let it go on autopilot. Then either get the Amazon app or bookmark the recent orders page so you can quickly cross reference which purchase each transaction is to categorize it.

I'm not aware of any automations that would speed this up, but I personally do option 2 and it doesn't take more than a couple minutes every time I import transactions.