Sundering Titan

• WWizards of the Coast2020-08-07
  Official Ruling
  Sundering Titan's ability isn't targeted. When it resolves, Sundering Titan's controller must choose one land for each basic land type (Plains, Island, Swamp, Mountain, and Forest), and then they are destroyed simultaneously.
• WWizards of the Coast2020-08-07
  Official Ruling
  If one of the basic land types isn't present, it isn't chosen. If the only land of a certain type is one you control, you must choose it.
• WWizards of the Coast2020-08-07
  Official Ruling
  If a land has more than one basic land type, it can be chosen more than once.
• WWizards of the Coast2020-08-07
  Official Ruling
  Players can't take actions in between the time you choose the lands and the time you destroy them. Notably, they can't activate mana abilities of those lands.

Rulings via Scryfall