Space after decimal comma in math mode

Question

This is actually my first time using Math mode in earnest. Without being able to put a finger on it, I am not really happy with the whole document (fractions are rather ugly, for starters). My main concern, however, is the space after the decimal comma – in math mode only. I appreciate your suggestions.

MWE:

\documentclass{article}
\usepackage[no-math]{fontspec}
\setmainfont{Noto Sans}
\setsansfont{Noto Sans}
\usepackage[italic]{mathastext}
\usepackage{eurosym}
\usepackage{enumitem}
\usepackage{amsmath,amsthm}
\usepackage{siunitx}
\DeclareSIUnit{\EUR}{\text{\euro}}
\sisetup{ 
            output-decimal-marker={,},
            group-separator={.},
            group-minimum-digits=4,
}
\begin{document}

Calculate the \textbf{present value} needed to obtain 1,400 € after 5 years at 6% compound interest.

\vspace{1em}\par
\textbf{Solution:}
\begin{enumerate}[itemsep=-3pt]
    \item $i = 6\% \Leftrightarrow q = 1,06$
    \item $n = 5$
    \item $FV = 1.400$
    \item $PV = FV \cdot q^{-n} \Rightarrow PV = \underline{\SI{1046,16}{\EUR}}$
\end{enumerate}


\vspace{1em}\par
2) Calculate the \textbf{interest rate} required to turn 1,000 € into 1,400 € within 5 years.
\vspace{1em}\par
\textbf{Solution:}
\begin{enumerate}[itemsep=-3pt]
    \item $n = 5$
    \item $PV = 1.000$
    \item $FV = 1.400$
    \item $i = \left(\frac{FV}{PV}\right)^{\frac{1}{n}}-1 \Rightarrow i = \underline{6,96\%}$
\end{enumerate}

\end{document}