In 1.X I used to use --json path/to/file.json with commands like conan create. With 2.0 I suppose I am expected to use --format json and redirect stdout to a file? So conan create --json x.json would turn into conan create -f json > x.json.
If that is the case, I believe it should be mentioned in Conan migration guide to 2.0 » Commands.