It seems Excel files (XLS) can have only 65536 rows, which is probably limitation of Excel itself. Is there a way to import spreadsheet data having more rows?
The XLS file has hard limit of 65536 rows. But the XLSX format supports rows up to 1,048,576 rows. According to my tests, it works and data can be visualized efficiently in Dashtera (unlike in Excel).
To have more rows than 1,048,576, please use CSV format file to import the data, or import several XLSX files.