I’ve been looking for examples of this in vocal scores but can’t find any offhand. If there is a better suggestion on how to do it in Dorico so a singer understands what is happen I would appreciate the suggestion.
On your macOS preferences>Keyboard, add the Unicode keyboard and make sure you can easily switch keyboards (either by the menu with the flags or a keyboard shortcut)
Enable Unicode keyboard when in Lyrics popover, keep alt key pressed while you input ff3f, the character should appear. Revert back to your normal keyboard
Another way to add a lyric extender line at the start of the second ending using Dorico 4.1 or later: Create a lyric consisting of several non-breaking spaces obtained by typing Shift-Alt/Opt-Space. Then select that lyric and use the command Edit>Notations>Lyrics>Edit Single Lyric to underline these spaces.