You get split Nautilus windows in GNOME the same way you get split anything windows: tile the window to the left (Super+Left or drag window until mouse touches

You get split Nautilus windows in GNOME the same way you get split anything windows: tile the window to the left (Super+Left or drag window until mouse touches the left screen edge), open new Nautilus window, tile it to the right (Super+Right or draw window until mouse touches the right screen edge). Presto.