Hi @David_Sotropa , welcome to the forum
The only way to achieve this is to set those custom field as local, i.e. do NOT checkmark the option âAdd field to your organisationâs libraryâ in the fieldâs edit settings. If the field has been already used in multiple projects, this option will be disabled, meaning you need to remove the field from all other projects except your internal project.
This will result in the fields only being available in your internal project, however they will not be visible in the task details to users who are NOT members of your internal project, which should be set to private for good measure if the fields contain sensitive information.
A really good article on this is: