Dialog Cards > Behavioural settings > Scale the text to fit inside the card.
This option makes it possible to resize a longish text to fit inside a card. Of course, a longish text then has such a tiny font that it becomes illegible, and of course the Dialog Cards activity is not supposed to consist of longish texts. However, for the purpose of crash-testing this activity (!) I have found the following bug.
Create a Dialog Cards activity with at least 2 cards. In Card 1 insert a long text. Check Behavioural settings > Scale the text to fit inside the card.