Welcome to the Online Community, spora5.
The ability to highlight any transactions in QBO is unavailable at this time. For easy tracking, I suggest exporting the report to Excel.
This way, you can add color to highlight the total amount owed by your customers. The process of exporting the data to Excel is similar to all reports.
If you already have one open, go to the middle part of the report and choose the Export icon to select Export to Excel. Once done, follow the on-screen instructions to transfer the data.
For additional resources, the Customise your financial reports article provides detailed instructions on how apply filters and ways to manage reports.
If there's anything else I can help find in QBO, leave me a comment below. I'm more than happy to assist further. Wishing you the best.