Glad you came here, @stylemaster1,
Yes, you can definitely upload more than 1 attachments in QuickBooks Online. All you need to do is press the CTRL button in your keyboard to select multiple files to attach.
To add attach files in the Attachments page:
To attach documents on transactions:
To get to know more about this feature, check out this article: Attachments in QuickBooks Online.
I also encourage you to visit our QuickBooks Online Australia Resource Page to get helpful tutorials and guides about our program. Click this link to our website: QuickBooks Online Australia Resource Centre.
If you need further help with this topic or anything about QuickBooks, let me know in the comment. I'm always here to help you. Have a wonderful day!