I'll be glad to help you in categorizing your receipts in QuickBooks, @gilesyone-gmail-.
In QuickBooks Self-Employed (QBSE), you can split downloaded banking transactions that aren't categorised yet. You can split them between business and personal, as an amount or percentage.
The option to split receipt that's you've manually entered inside QuickBooks is unavailable. However, you can manually import your transaction in QuickBooks using a CSV file. This way, you can categorise and split it.
Here's how:
- Go to the Profile ⚙ icon and select Imports.
- Click Import transactions.

- Follow the onscreen steps to upload the CSV file.
- Select Import.
Please take note that before you import your transaction, make sure that the amount you've entered is similar to the amount in your receipt. This way, you can split its amount correctly. Once your transaction is in QuickBooks, you can now attach the receipt and categorise it.

I've also included an article that will guide you in splitting your transactions in QBSE: How to split a single transaction between business and personal, or into multiple categories.
The Community always has your back, so please let me know if you need further assistance. Have a great weekend, and stay safe.