It is not possible to directly sort the transaction list with splits by customer, KMBLRPC. I will share further details below.

You can add the customer column to the report. However, you cannot directly filter it to show billable expenses. Instead, you can filter by the associated vendor to display transactions related to your customers. Let me show you how:

1. Go to the Reports menu and select the Transaction List with Splits report.
2. In the upper-right corner, tap the Customize button.
3. Click the Change columns link, then place a checkmark next to the information you want to see, specifically the Billable and Customer columns.
4. From the Filter dropdown, choose the transactions in the Transaction Type section.
5. Select the associated vendors from the Name section.
   
6. Click Run report to display the data.
   

For the time being, I suggest forwarding your feedback to our product development team regarding the option to sort transactions by customer in the Transaction List with Splits report. They can review it and may consider implementing it in the future. Here’s how:

1. Go to the Gear icon at the top and click Feedback.
2. Enter your feedback and product suggestions.
3. Tap Next to submit them.

I've also included this article for your reference to save your reports to Excel, which will provide more options for personalizing your company's data: Export your reports to Excel from QuickBooks Online.

We greatly value your feedback as it helps us enhance our program. Should you have any further questions regarding customizing your reports, please feel free to contact me. I'm here to assist you.