You don't need to create a separate transaction for the fees if you're using the Connect to Square connector app, victoria48.
Sales transactions are downloaded individually as sales receipts. Each downloaded entry includes a breakdown of the sales, tips, discounts, refunds, taxes, and fees, as shown in the screenshot.
You can specifically see the details when categorizing after the transactions are downloaded from Square. Here's how:
- Go to the For review tab under App transactions.
- Select a transaction to see more details.
- Look at the lower-right-hand corner to see the fee breakdown.
- From there, you can either add it to your register or match it with an existing transaction.

You can read more details about this here: Connect your Square account to QuickBooks Online.
If you're not using the Connect to Square app, you can edit the invoice and manually add the fees. Go to this article for a step-by-step guide: Enter a bank service fee while using a third-party merchant service in QuickBooks Online.
Let me know if you need anything else.