Hide-the-pain Harold is always a winner. For everything.

Embed a Minecraft parkour video in one corner and you will have undivided attention

Somebody shoving representations of thoughts and fears into the trash, or a locker. Get those negative things out of here.

I would try clipart of brains, thought bubbles, people conversing, and person thinking.

When I do work PowerPoints I purposely use the cringiest most cliche stock photos, with their watermarks still on, because I think the irony of it acknowledges the awkwardness of work presentations and makes me seem less pretentious as a presenter. Unfortunately, this trick may not be so fitting depending on what exactly you're covering for mental health. On the other hand, humor can be a great antidote to mental pain, so maybe that could work. Idk.

Ummm let's see...you could try to structure the presentation so it has some sort of metaphor or arc to it. You could have pictures of a tree in a dark field, sunny field, rainy field, rainbowy field, depending on the context. Or like, wilted flower, sad flower, thriving flower, etc. That actually seems very sad or possibly just generic and trite now that I think about it, so maybe that's also not ideal. You could do something more abstract with just the background colors, a gradient like progression. That'll be hard to do well without some decent color theory knowledge though imo.

You could look up famous movie depictions of whatever mental state you need and use screen caps from those. Fictional characters are a great way to evolve empathy from people.