Welcome to Workfront! I think if you refer to the collections help
article, this is covered in the limitations section.
https://one.workfront.com/s/document-item?bundleId=the-new-workfront-experience&topicId=Content%2FReports_and_Dashboards%2FReports%2FText_Mode%2Freference-collections-report.html
Unless I miss my guess, you cannot control the order. You can certainly
try and throw in the below two lines at the end of your text mode, but
if/when it doesn't work, this would be why. sortOrder=1sor...