I just tested the Fields and Text block on a local site and I could add line breaks wherever I wanted (shown in the preview in the screenshot), and these were respected on the front end.
You just type Enter where you want a line break.
Obviously you would have done that, but I'm not sure what specifically are the circumstances where you are trying to use Enter for a line break but cannot.
In your screenshot you seem to have switched away from the normal View to display the shortcodes instead of the preview.