A few more I just thought of, and in addition to the other list BeamBrain made:

Spiritfarer (Entirely about learning to accept mortality, mourning, aging and death, but VERY whimsical and playful on the surface. You are a sweet young girl who is actually the captain of the ferry of death, giving the dead their last wishes before leading them into oblivion... by farming and cooking and sight-seeing)

Gris (more dreamlike than whimsical, but again reveals through the game it is meant to be explicitly about trauma)

The next three I haven't played, but by what I know of them...

Farewell North (About healing after trauma, and admittedly as the name implies, saying the last goodbye, but on the surface about a dog making the world colorful by shepherding, freeing wildlife, etc.)

Beacon Pines (another story-book kind of adventure with furry animal characters on the surface but has some really dark twists about trauma and existential dread underneath).

Wanderstop (a tea shop in a magical forest! Oh wait it's dealing heavily with burnout and psychological pain/trauma.)

The list just goes on.

There's even studies that have been done addressing how trauma in indie games is a thing.!

Trauma Representations in Video Games

Over the last few years, the videogame community has seen an increase in the visibility of indie games, particularly ones that focus on serious subjects. Given the name “empathy games” by Minority Media’s Vander Caballero in his 2014 GDC talk, this sub-genre is known for its intense and meaningful narratives that often bring to light traumatic experiences.

Also...

Trauma in Games: Narrativizing Denied Agency, Ludonarrative Dissonance and Empathy Play