Hi alect,

Yes, you are correct. Currently, the list report like Transaction List by Customer has no option to Expand or Collapse the report like we have with summary report like Sales by Customer Summary. Please note that this option not available in all reports yet. If you prefer to generate a list report, you can click on the drop-down arrow located beside the customer name to expand or collapse the details on it. 

I know how handy that feature would be in QuickBooks Online. I encourage you to submit feedback so our product development team knows exactly how important this functionality is for your business. They take your suggestions into consideration when implementing new features and making improvements to existing ones. You can submit your valuable feedback by going to Gear icon and select Feedback.