Thank you for your reply.
In general this is not a real issue, except for cells representing a date. A cell containing a date has a numeric value. Example:
// Cell A1 contains the date 01-01-2023, with cell type "date"
$cellContents = $xlsx->getCell("A1");
echo $cellContents["value"];
// this gives the integer 44927
// Cell A2 contains the number 44927, with cell type "number"
$cellContents = $xlsx->getCell("A2");
echo $cellContents["value"];
// this gives the integer 44927
Converting 44927 to 01-01-2023 is not hard knowing the Excel 1900 date format. But, without knowing the cell format, we do not know if the value represents a date or an integer.