Thanks for taking the time to reach out to us. I'm here to help and provide some insights about scanning expense receipts in QuickBooks Online (QBO).
There's no way to scan a bunch of expense receipts once you're using the QuickBooks application since this is working as designed so you can select the correct transactions. However, if you're trying to add multiple attachments list transactions in QBO, you can follow the steps below:
Select the Gear icon.
Under Lists section, choose All Lists.
At the upper left, select Attachments (clip icon).
On your keyboard press Ctrl to browse and select the document you want to attached, then select Open.
I also added some articles for your additional reference: