How to visualize iTunes "group" column on MP3tag?

[ohrenkino]

Check the extended tags dialogue with ⌘T and see which field name is used for the data.
The add a column for the field in the file list and/or that field in the tag panel as described in the documentation

Customization of Tag Panel and File List

Mp3tag supports flexible tagging, which means that the tag fields available on the Tag Panel on the left and as columns in the File List are not fixed. While you can reference any field which is, e.g., listed in the extended tag dialog as name via a placeholder %name% in Mp3tag, it's also possible to customize the UI using these placeholders. Customizing the Tag Panel The Tag Panel is the sidebar on the left of the File List that shows the fields to enter metadata. Besides the standard field…