Am setting my default style as follows
$style_default = (new StyleBuilder())
->setFontName('Calibri')
->setFontSize(11)
->build();
$writer = WriterEntityFactory::createXLSXWriter();
$writer
->openToBrowser($workbook_name . '.xlsx')
->setDefaultRowStyle($style_default);
However, any cell added that has no content (WriterEntityFactory::createCell('')) is using the default font-size of 12 pt rather than my preset default of 11. Adding a space (WriterEntityFactory::createCell(' ')) will use the correct font (but then you have a cell with a textual space in)
Explicitly setting the style also does not work WriterEntityFactory::createCell('', $style_default)