Answer
That advanced section is part of a built-in DIALOG, not a genuinely separate customizable Page reachable through Page Designer, so it isn't directly editable or hideable through the normal Page Designer customization mechanism the way an ordinary page would be. That section only appears at all because the specific Document Class in question has its Number Generator setting configured as 'Advanced' rather than 'Standard.' If the goal is simply to prevent users from seeing or interacting with that advanced number-choice section, the practical fix is to change the affected Document Class(es)' Number Generator setting to 'Standard' instead, which removes the need to hide anything in the dialog at all, rather than trying to customize the dialog itself.