In GoodNotes 5, there was initially an experimental feature called Flashcards - which, after a lot of feedback and tweaking, we later re-released as Study Sets. After the release of Study Sets, Flashcards became a legacy feature, and in Goodnotes 6, we have retired this legacy feature.
If you are looking to convert your old legacy Flashcard decks into Study Sets in Goodnotes 6, we have a support article for this: Converting Legacy Flashcards into Study Sets. Alternatively, if you have feedback on how we can improve the Study Set feature, please don't hesitate to share this with our Customer Support team via this link.
We would like to thank all users who tried out Flashcards in GoodNotes 5, and gave us feedback which led us to develop Study Sets!