I would like to have this kind of table
\documentclass[12pt]{standalone}
\usepackage{spreadtab}
\usepackage{siunitx}
\usepackage{tabularx}
\usepackage{eurosym}
\usepackage{numprint}
\usepackage{booktabs}
\begin{document}
\begin{spreadtab}{{tabularx}{\linewidth}{XS[table-format=4.2]l}}
\toprule
@{Was} & @{Betrag [\euro]} & @{Belegart} \\
\midrule
@Nice People Charity & 300 & Spendenbescheinigung @\\
\midrule
@Summe [\euro] & \textbf{\numprint{:={sum(b2:[0,-1]) }}} & \\
\bottomrule
\end{spreadtab}
\end{document}
but the money amount in the second and last lines are not aligned as they should:

It seems to me that the last row does not get included by siunitx. How can I get this to work? Tinkering with table-format=4.2 does not really count, because then I have the same problem with another table somewhere (the whole thing is in a custom made command, but let's keep it simple for now).
Bonus if one can get me this to work with
\usepackage{tabu}
instead of tabularx. I'd like to use XS[...] or X[c]{S[...]} or whatever the current command is... ready through Stackexchange got me a little confused... sorry.
I tried using
\usepackage{dcolumn}
which did not work, because it does not support \euro from
\usepackage{eurosym}
Edit: From
siunitx: aligning numbers by decimal points in tables doesn't work for bolded or italicized numbers
and
siunitx: How to get bold, aligned entries and how to align when units differ in length?
I got that the reason the numbers are not aligned are because of the boldness and \numprint. However, I have not been able to get the suggestions to work – propably because I am additionally using spreadtab.
\numprintis. I'm not familiar with the package, but it seems that it's a number formatting package. Butsiunitxalso does number formatting, so it's hard to make a case that one needs to use\numprinthere. Can you clarify, please? – Faheem Mitha Sep 10 '21 at 07:40\textbf, it would not have been formatted. Maybe I did not know how to format it with something else than numprint, but maybe the issue would have remained because of\textbf. – Make42 Sep 10 '21 at 17:47siunitxinstead ofnumprint. It looks likesiunitxis a superset in terms of features. Though without carefully looking at both packages I cannot be sure, of course. Having said that, there still seems to be an issue using\numprintwithsiunitxv3 in TL 2021. Can you still reproduce it with TL 2021? – Faheem Mitha Sep 10 '21 at 18:18