I saw this in the Survey123 help, which is exactly what I need:
The bind::esri:fieldType column also accepts the null value, which will cause the question to be omitted from the feature service created. While the question will still be present in your survey and behave normally, the answer will not be submitted to the feature service and will not be present when reviewing responses. This is ideal for calculations, constraints, or other questions that need to be present for presentation purposes but aren't needed in the results. The following question types do not support a null field type: select_one or other, select_multiple or other, image, hidden
But I cannot figure out how to do so! Null is not an option in the dropdown, and when I type in "null" it's not accepted. Please advise, thanks.