Remove title separator in Beamer Metropolis theme

Question

I would like to disable the zero-height box separator between the subtitle and the author, inside the title slide. On the Metropolis documentation I found only the way to change the color of the title separator, but not to remove it. How can I do? This is my code

\documentclass[aspectratio=169]{beamer}
\usetheme[progressbar=foot,numbering=none]{metropolis}
\usepackage[italian]{babel}
\usepackage[utf8]{inputenc}
\usepackage{centernot}
\usepackage{enumerate}
\usepackage{array}
\usepackage{fontspec}
\usepackage{ semantic }
\usepackage{siunitx}
\usepackage{framed}
\usepackage{graphicx}
\usepackage{proof}

\author{Prof. Marco Doninelli}
\title{Limiti di successioni}
\subtitle{Definizione di successione}
\date{}

\begin{document}
    
\begin{frame}
\maketitle
\end{frame}

\end{document}

which produces

Answer 1

That orange horizontal line separating subtitle and author is produced by the beamer template title separator, a new template defined by theme metropolis (see its source file beamerinnerthememetropolis.sty).

Simply redefining that template solves the problem.

\documentclass[aspectratio=169]{beamer}
\usetheme[progressbar=foot,numbering=none]{metropolis}

\author{Prof. Marco Doninelli}
\title{Limiti di successioni}
\subtitle{Definizione di successione}
\date{}

\setbeamertemplate{title separator}{}

\begin{document}
    
\begin{frame}
\maketitle
\end{frame}

\end{document}

To adjust the vertical space between subtitle and author, you can try

\setbeamertemplate{title separator}{\vspace{-10pt}\par}