Unlike other masks, which use a "puzzle matte" approach of a single layer with different colors in them to denote different objects, materials, etc., Cryptomatte places the mask for each item in its own separate layer in the file (the CXR, which you can rename to EXR). The layers will be named after each object, or layer (in the host application), or name and layer, etc. as determined by what options you checked in the cryptomatte render element, and will contain a greyscale mask for that object (or layer, or etc. depending on what you checked in the cryptomatte settings). The fact this color map type layer exists is just a side effect of the calculations, and is not the actual cryptomatte data in usable form, and can be ignored (and deleted, even, once in Photoshop).
To see these layers, the application you use to load it MUST understand cryptomatte data, otherwise you won't see them. For Photoshop, this would mean using Exr-IO, which in the latest version can read and translate cryptomatte data. There is other software out there that has a native understanding of cryptomatte, such as Nuke, but I don't have that so can't comment on the workflow :)
You can check tutorials like
https://youtu.be/apk11RaFKo8?t=247 as an example (also see the 5 minute 40 second mark, where they copy and paste the cryptomatte mask for an object into the mask for an adjustment layer, which is how you use it to refine, say, exposure for a particular object, or color tint, or saturation, or whatever adjustment layer you are using).
Hope that helps! Naturally when time allows, we'll be making our own tutorials going through from start to finish too :)