Hey versionz
- Create a new Field Group
- On the “Location” metabox, set “Show this field group if” “Attachment” “is equal” “all”
- You’re done
All field you’ll add will now only display for attachments (including when selecting for edit an image inside a gallery field).
(I’d have preferred if a new post would have been opened, since this question/answer doesn’t simplify the reading of this already complex topic we are in 😉 )