The Legacy Cryptomatte node doesn't work in GPU execution mode if
Precision is set to Auto. That's because the colors picked from the Pick
layer might be in half precision and thus will not match the colors in
the Cryptomatte layers. This is due to the compositor using the
context's precision for Viewer outputs as opposed to the precision of
the image that actually needs to be viewed in the Viewer node.
To fix this, we set the Viewer node precision to be the precision of its
input, that way, the Cryptomatte pick layer will be output in full
precision as intended.
Pull Request: https://projects.blender.org/blender/blender/pulls/128495
ccab8005f6