Does anyone here have experience with the rules for mental stress in the 2024 Dungeon Master's Guide?

I am planning on giving them a try in a horror-oriented sequence, though I am not quite sure what sort of saving throw to call for, or what the DCs and Psychic damage should be.

4th-level PCs are walking through a (metaphorical, but perhaps literal) hellscape of a battlefield. Some magical cataclysm has slaughtered innumerable soldiers and left behind masses of corpses and rivers of blood. The sky is a deep red, and enormous eyes watch from above. A very stressful sight (and smell), at least by real-world standards. Is encountering this an Intelligence, Wisdom, or Charisma save? What should the DC and Psychic damage be?

Later, those same 4th-level PCs are walking through the remains of a town. These innocent civilians had it even worse in the calamity. Their bodies are mangled beyond recognition, heaps of bloody flesh and bone. Likewise a stressful sight (and stench), but is it much worse than the previous one? Is encountering this an Intelligence, Wisdom, or Charisma save? What should the DC and Psychic damage be?