This is what you find in the xl/worksheets/sheet1.xml when saving excel with freezed rows
<sheetViews>
<sheetView tabSelected="1" workbookViewId="0">
<pane ySplit="1" topLeftCell="A2" activePane="bottomLeft" state="frozen"/>
</sheetView>
</sheetViews>
This can be dynamically added using xlsxAdd xlsx transformation helper like this
{{#xlsxAdd "xl/worksheets/sheet1.xml" "worksheet.sheetViews[0].sheetView"}}
<sheetView tabSelected="1" workbookViewId="0">
<pane ySplit="1" topLeftCell="A2" activePane="bottomLeft" state="frozen"/>
</sheetView>
{{/xlsxAdd}}
Playground example
https://playground.jsreport.net/w/anon/nJiWyZq9