The state:modified method needs to compare your current manifest with another manifest
So you have to save the old manifest in a folder and pass the folder’s path to the state flag
$ dbt run --select model_b --defer --state prod-run-artifacts
The state method is used to select nodes by comparing them against a previous version of the same project, which is represented by a manifest. The file path of the comparison manifest must be specified via the --state flag or DBT_STATE environment variable.