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.
07-08-2020
wotc
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.
07-08-2020
wotc
If a land has more than one basic land type, it can be chosen more than once.
07-08-2020
wotc
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.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.