Let me share some clarification about exporting a statement of account in QuickBooks Online.
Currently, an option or keystroke to export statements in that format is unavailable. As a workaround, you can either run the Customer Balance Detail or Summary report and download the data to Excel.
Here's how:
On the left panel, click Reports.
Scroll down to the Who owes you section.
Select Customer Balance Detail or Customer Balance Summary.
Press Customise.
Make the necessary changes.
Hit Run report.
Click the export icon, then choose Export to Excel.
Since you can only download customer statements as PDF, I also recommend searching for a third-party application to convert the file to Excel.
Additionally, here are some helpful references that you can check out about how to customise statements and reports in QuickBooks Online: