Thank you for your reply. If I may elaborate on my question, I see that if a feature class is enabled for attachments then you can attach photos in Field Maps without interrupting the collection of the line vertices. However you cannot view the location of the photos or enter notes about each photo.
On the other hand, if you relate a point table to a line feature class, and then enable the point table for attachments, you can view the locations of the photos and add add notes for each photo. But in this case you must submit the line data before you can access the related point table and take a photo. Same issue if you have an independent point feature class enabled for attachments.
But it is not possible to capture photos as points with attributes at the same time as you are collecting a line?