Misplaced \cr MWE

% \documentclass[sans,math,palette=es]{bmc}
\documentclass{article}

\usepackage{etoolbox}
\usepackage{booktabs}
\usepackage[table]{xcolor}

\colorlet{text}{black}
\colorlet{page}{white}
\colorlet{tableheadcolor}{orange!30!page}

% Use of \showrowcolors and \hiderowcolors is an idea from Ulrike
% Fischer's answer here: <https://tex.stackexchange.com/a/494954/73317>
\renewcommand{\toprule}{%
    \showrowcolors
    \arrayrulecolor{text}\specialrule{\heavyrulewidth}{\abovetopsep}{0pt}%
    \arrayrulecolor{tableheadcolor}\specialrule{\belowrulesep}{0pt}{0pt}%
    \arrayrulecolor{text}%
    \rowcolor{tableheadcolor}%
}

\apptocmd\midrule{\hiderowcolors}{}{\FAILED}

\makeatletter

\let\@BTrule@ORI=\@BTrule
\let\my@BTrule=\@BTrule

% Modified version of \@BTrule that doesn't do \vskip\@aboverulesep, for use
% when the corresponding vertical space should be coloured.
\patchcmd{\my@BTrule}{%
    \ifnum\@lastruleclass=\z@\vskip\@aboverulesep\else
  }{%
    \ifnum\@lastruleclass=\z@\else
  }{}{\FAILED}

\let\@arraycrORI=\@arraycr

\renewcommand*{\@arraycr}{%
  \@ifnextchar\midrule\my@endtablehead\@arraycrORI
}

\newcommand*{\my@endtablehead}{%
 \@arraycrORI[\aboverulesep]% this colours the additional space with the
                            % current row color
 \noalign{\global\let\@BTrule\my@BTrule}% temporarily modify \@BTrule
 \midrule
 \noalign{\global\let\@BTrule\@BTrule@ORI}% restore it
 \@gobble % gobble the following \midrule (which *must* be there!)
}

\makeatother

\rowcolors{1}{tableheadcolor}{tableheadcolor}

\title{Test}
\author{Auth}

\begin{document}

\begin{tabular}{>{\hspace{3pt}\normalsize}l>{\hspace{5pt}}*{5}{p{7.9em}}}
    \toprule
    Category & \multicolumn{5}{l}{\normalsize Packages} \\
    \midrule
    General & etb & xpt & sil & ifd & geom \\
    & tts & ttc & frm & tps & clc \\
\end{tabular}

\end{document}