Can I underline the end of my hero headline?

Yes. Open the page, open its Hero block, and in the Headline section set Headline Marker to Last two words or Whole headline. A thick line in your theme's highlight color runs under those words, and follows them onto a second line if the headline wraps. Off, the default, leaves the headline plain. It works on every hero layout: full width, Image Beside Text, and a hero with no picture.