Galadriel, Light of Valinor

• WOTC Official Reminder Textofficial rules
  Scry — Look at the top N cards of your library, then put any number of them on the bottom of your library and the rest on top in any order.

• WWizards of the Coast2023-11-03
  Official Ruling
  The phrase "that hasn't been chosen this turn" refers only to that specific Galadriel, Light of Valinor. If Galadriel leaves the battlefield and then returns to the battlefield later in the turn, it will be a new object with no memory of the modes chosen when it was previously on the battlefield.
• WWizards of the Coast2023-11-03
  Official Ruling
  If all three modes have been chosen this turn, Galadriel, Light of Valinor's triggered ability is removed from the stack with no effect.
• WWizards of the Coast2023-11-03
  Official Ruling
  It doesn't matter who has chosen any particular mode. For example, say you control Galadriel, Light of Valinor and have chosen the first two modes this turn. If an opponent gains control of Galadriel, that player can choose only the third mode this turn.
• WWizards of the Coast2023-11-03
  Official Ruling
  If multiple creatures enter the battlefield simultaneously, you must still choose different modes for each instance of the triggered ability that's put onto the stack. If more than three creatures enter the battlefield simultaneously, that choice is made only for the first three.

Rulings via Scryfall