From the opened card, click on the "+" button. The card creation popup will open.
Fields configured in the sub-list only
In the Administration interface, an option is located next to each sub-list of a card. It allows you to define which fields will be displayed in the card creation popup.
By checking this option, the fields displayed in the creation popup will be the same as the columns displayed in the sub-list.
Otherwise, the default fields configured at the card level will be displayed.
If mandatory fields have been configured by default but do not appear in the sub-list configured fields, they will be ignored and you will still be able to create your card.