Hello Peter,
No—XMLports cannot import Excel (.xlsx) files, in NAV 2016 or Business Central; they only support XML (and CSV-style text). If you need Excel input, the practical options are to convert the file to CSV and import it, or use RapidStart / Configuration Packages, which natively work with Excel. Importing true .xlsx files is only possible via custom development (Excel Buffer + .NET/Open XML), which is heavier and usually not recommended unless Excel format is mandatory.
Regards,
Oussama Sabbouh