It's possible you're thinking of the Lost Zone mechanic, which was introduced in the Sword & Shield - Lost Origin expansion.
Here's how the Lost Zone works:
* Cards sent to the Lost Zone: Certain cards and abilities may send cards from your hand, field, or discard pile to the Lost Zone.
* No access to Lost Zone cards: Once a card is in the Lost Zone, it is completely out of play. You cannot access it for any reason, even if you have an ability that usually allows you to recover cards from the discard pile.
* Permanent loss: Cards in the Lost Zone stay there for the entire game. They cannot be returned to play.
The Lost Zone mechanic introduces a new layer of strategy to the game. You can use cards that send your opponent's Pokemon to the Lost Zone to weaken their team, or use cards that benefit from sending your own cards to the Lost Zone to achieve a strategic advantage.
Let me know if you have any more questions about the Lost Zone or any other Pokemon card mechanics!