The Flashcards of GoodNotes 5 have now been removed in GoodNotes 6 and replaced with Study Sets, but Flashcards have a lot of advantages compared to Study Sets:
1 . You can have an overview of Flashcards in thumbnails while seeing both the question and the answer (in Study Sets you only see the question). This helps with studying and having an overview of the set to see if it is done correctly.
2. The questions and answers are easier and quicker to create in Flashcards by writing and cutting and pasting as fewer steps are needed as the flashcard is immediately editable (in Study Sets you have to press edit every time for both question and answer, which takes up lots of time - if you do hundreds of study sets cards it takes forever)

Study Sets are good for other reasons especially for studying, but Flashcards are really so much better for the creation of the cards and having an overview of the set.

Please re-instate flashcards in GoodNote 6:)