2022-02-18 : Discarding the card is part of the cost to activate a channel ability.

2022-02-18 : If a channel ability requires a target, you may not activate it without a target just to discard the card.

2022-02-18 : The creature or planeswalker card you return to your hand is not chosen until after you mill three cards. You may choose a creature or planeswalker card from among all the cards in your graveyard, including the milled cards.