[_vufv]

Also, idempotency of a tool is a desired property that tool devs often invest a lot of effort in maintaining. Initializing default config on the first run is a trivial way to break it.

It's much better to just have a sane implicit default value for each setting when config is not present. Then you can list the default config in your docs or offer a CLI flag --print-default-config or --copy-default-config.

[Y_Y]

Creating a file if it doesn't already exist is idempotent.

[account42]

Only if you always create the file with the same contents, which is almost certainly not going to be true when the software evolves and adds new options.