Hi DoctorDutch ,
Apologies for any inconvenience caused.
You can use the "Stock quantity steps" option (just below the "Decimals in Stock Quantity" option). Just set it to 1. It should work.
Please note that customers will still be able to set the quantity manually with decimals (that is what the "Decimals in Stock Quantity" option is supposed to do).
Best Regards,
José Andrés