I have a view with hidden fields, but when I open the card form view, the columns are visible, why?

“If the columns are visible in card form view even when they are hidden in the view, this is due to the fact that the option ‘also hide in card view’ has not been checked in the field restrictions settings.

To resolve this issue, make sure to check this option so that the columns are hidden both in the view and in the corresponding card form view.

More details here: Restrict access to a column by view