In the respective upload field settings you can determine for which product and its variants the upload field should be displayed.
Select > Show button on products that match any of these conditions >
Product is one of > Choose product(s) > Sample Product
Result: The UploadField will be displayed for Sample Product
Select > Show on variants that match any of these conditions >
Input you value for example: Color > Equals > Red
Result: The UploadField will be displayed for Color: RedNow the button will only be visible for Sample Product > Color: Red
Don’t forget to save!