"The ghosts only visible through camera" is just such a long running trope that I couldn't not think about it. With the eeriness and the silent-hill-esque use of thick fog. One possibility would be to somehow embrace the trope while also averting from it? :thinking:
Like... hmm.. one good example comes to mind:
In Outer Wilds you can only see this "ghost matter" while looking through a camera. It's a kind of radiation that kills you if you walk into it.