You can create separate expenses by having multiple line items and marking these items as billable to donors in QuickBooks Online (QBO). Please make sure that you have turned on the billable feature in QBO.
Let me show you how:
Go to + New and then create an Expense.
Provide all the necessary details especially, the donor's name and amount of expense per line item.
Check the box on the Billable column.
Hit Save and close.
Also, I've added video article guides on how to handle expenses in QuickBooks Online: