Today, when you have an existing Board with an existing Form, and if you add a new Column to the Board, it will automatically add the new column as a hidden question in the Form Builder. Here’s the only reference I could find for this functionality in the Help Centre
When you have long, complex, and multi-branching forms, the inclusion of these hidden questions automatically created for new columns get in the way and impact the UI/UX of the Form Builder.
We want the ability to stop Monday from automatically adding newly created columns to the Form, even if its as a hidden question.