Found it:
kopia snapshot list --json --json-indent --config-file=$HOME/.config/kopia/repository.config "$user@$host:$pathToBeSnapshotted" | grep "id" | head -n1
"id": "c5488bd7509fa100aa10c9ede4fcbf57",
So I echo @kapitainsky : this seems like a bug… at least in proper output in the CLI, GUI.