Unable to queue when your default deck meets the requirement
Bug reproduction steps
I set a duel links deck as default and tried entering the Duel links Ranked queue and it said “Invalid amount of cards” my deck has 20 cards in the Main Deck and 5 Cards in the Extra Deck and it follows the Duel Links 2020 Banlist.
Screenshot OR error code
I should be able to enter the queue because the deck is valid
When joining the Duel Links ranked, only the cards released in Duel Links are allowed. This is why you got invalid deck because some of the cards in your deck are not released in Duel Links. This is probably one of those synchro monsters.