You're doing it ALL wrong.
First, drag the Cethleann.DataExporter.exe file from CethleannStandalone_netcore30 folder, drop at your cmd and type -g DissidiaNT -P Windows --yshtola. Don't type out-dir "game-dir".
Then, drag the New Folder from your desktop and drop at your cmd.
And lastly, drag the entire DISSIDIA FINAL FANTASY NT folder, drop at your cmd and press ENTER. Not the COMMON folder.
I hope this REALLY helps you out. Look carefully at my attachment shown as an example.
First, drag the Cethleann.DataExporter.exe file from CethleannStandalone_netcore30 folder, drop at your cmd and type -g DissidiaNT -P Windows --yshtola. Don't type out-dir "game-dir".
Then, drag the New Folder from your desktop and drop at your cmd.
And lastly, drag the entire DISSIDIA FINAL FANTASY NT folder, drop at your cmd and press ENTER. Not the COMMON folder.
I hope this REALLY helps you out. Look carefully at my attachment shown as an example.