var originatingController: ResultsTableViewController? shouldn't be DecksTableViewController? I changed it and it works now! Thanks a lot @Claude31!

>Where is result row (a cell in which table) ? I suppose it is in the table of ResultsTableViewController ? Do I understand correctly that this table can contain either Decks or cards ? - Yep, right, results are cells in ResultsTableViewController, there might be decks or cards, depending on scope. >Is behaviour different for decks or cards, or is it the same "nothing happens" ? - Yes, for both nothing happens. >Did you check identifiers are effectively "cardsVC" and "cardDetailVC" (with same upper/lowercase) - Yes, I checked. This is the output: navigation controller is nil, I also tried to embed ResultsTableViewController with navigation controller, but it didn't help. didSelect scope Optional("Decks") indexPath [0, 0] Decks cardsVC instantiated, with selectedDeck Optional(Deck { _id = 60e98c5da7d8064df3298f68; name = Greetings; dateCreated = 2021-07-10 12:02:37 +0000; layout = frontToBack; autoplay = 0; cards = List<Card> <0x283afcfc0> ( [0] Card { _id = 60e98c63a7d8064df3298f6c; front = hello; back = ; dateCreated = 2021-07-10 12:02:43 +0000; audioName = (null); }, [1] Card { _id = 60e98c6aa7d8064df3298f6d; front = good evening; back = ; dateCreated = 2021-07-10 12:02:50 +0000; audioName = (null); } ); }) self.parent?.navigationController nil didSelect scope Optional("Cards") indexPath [0, 0] Cards cardDetailVC instantiated, with selectedCard Optional(Card { _id = 60e98c6aa7d8064df3298f6d; front = good evening; back = ; dateCreated = 2021-07-10 12:02:50 +0000; audioName = (null); }) self.navigationController nil