I turned off all other passes in order to be able to include a small sized .exr.
In passes. I’m not utilizing any layers. The “View Layer” layer (man…) is already the selected one the the file version where I add the mist. Same as in the tutorial, but he doesn’t show his whole node other than he has more passes activated.
Mist is a normalized depth output. You control the normalization in the world tab, and you can set the camera to show the limits. I’m guessing it’s outputted as a float and stored in the Mist channel at rendertime. If you want to use it, you have to do it in post.