Contacts, enums for extended contact fields, enums for enums for extended contact fields & Google Apps Script. HELP

It took some time before I understood how I had to do it, adding extended fields to a contact in Google Contacts:

function pieterPukOne(){
 
  ContactsApp.getContact("puk@pieterpuk.xyz").addCustomField(ContactsApp.ExtendedField.SENSITIVITY,"CONFIDENTIAL");
  ContactsApp.getContact("puk@pieterpuk.xyz").addCustomField(ContactsApp.ExtendedField.GENDER,"MALE");
  
}

The first problem is dat I can not see the newly added custom fields in the contact information of the contact Pieter Puk.

The second problem is the result of 'searching for' contacts by custom field:

function pieterPukTwo(){
 
  Logger.log(ContactsApp.getContact("puk@pieterpuk.xyz").getCustomFields().map(function(customField){return customField.getValue()}));
  Logger.log(ContactsApp.getContact("puk@pieterpuk.xyz").getCustomFields(ContactsApp.ExtendedField.GENDER)[0].getValue());
  Logger.log(ContactsApp.getContactsByCustomField("puk pieter#no problem at all","Zaaknaam").map(function(iets){return iets.getFullName()}));
  Logger.log(ContactsApp.getContactsByCustomField("CONFIDENTIAL","SENSITIVITY").map(function(customField){return customField.getFullName()}));
  Logger.log(ContactsApp.getContactsByCustomField("MALE","GENDER").map(function(customField){return customField.getFullName()}));
 
}

Strange:

Contact Pieter Puk has three custom fields but the only 'custom field' returned with ContactsApp.getContactsByCustomField is 'Zaaknaam'.

I do not understand what I am doing wrong

The third problem is that I do not know what can be done with for example the extended field SENSITIVITY.CONFIDENTIAL.

Does it limit the way contact information can be used?