Option 1: If the field does not have any border that must also be hidden, use a conditional format to change the field's text color to match that of the background or set the text size to extremely large. This hides the content of the field.
Option 2: If you need to hide a field with a border so that even the border is not visible, you need to use a "visibility trick". One way is to use a portal to a related record. By changing the value used in a portal filter expression or in the portal's relationship the contents of the portal can seem to appear and disappear. You can make the outline of the portal transparent so that it is not apparent that the field is inside a portal.
Option 3: Another visibility trick is to place the field on the tab of an invisible tab control. (Set tab control's properties to match layout background.) A script trigger then uses Go To Object to select the appropriate tab to hide/reveal the field. This requires assigning an object name to each tab.