{
 \begin{bNiceArray}{*{6}c*{6}c}[columns-width=8mm, margin]
    \Block[borders={bottom,right,tikz=dashed}]{6-6}<\LARGE>{\mathbf{E}_{6m}} & & & & & & 
    \Block[borders={bottom,right,tikz=dashed}]{2-4}<\Large>{\mathbf{O}} & & & & 
    \Block[borders={bottom,tikz=dashed}]{2-2}<\Large>{\mathbf{E}_{2m}} \\
    & & & & & & & & & & \\
    & & & & & & 
    \Block[borders={bottom,right,tikz=dashed}]{4-4}<\Large>{\mathbf{E}_{4m}} & & & & 
    \Block[borders={bottom,tikz=dashed}]{4-2}<\Large>{\mathbf{O}} \\
    & & & & & & & & & & \\
    & & & & & & & & & & \\
    & & & & & & & & & & \\

    \Block[borders={bottom,right,tikz=dashed}]{5-1}<\Large>{\mathbf{O}} & 
    \Block[borders={bottom,right,tikz=dashed}]{5-5}<\LARGE>{\mathbf{E}_{5m}} & & & & & 
    \Block[borders={tikz=dashed}]{6-6}<\Large>{\mathbf{E}_{6m}} & & & & & \\
    & & & & & & & & & & \\
    & & & & & & & & & & \\
    & & & & & & & & & & \\
    & & & & & & & & & & \\
    
    \Block[borders={bottom,right,tikz=dashed}]{1-1}<\Large>{\mathbf{E}_{m}} & 
    \Block[borders={bottom,right,tikz=dashed}]{1-5}<\Large>{\mathbf{O}} & & & & & & & & & & \\
\end{bNiceArray}
}

可以试试这样...

\documentclass[12pt]{ctexart}
\usepackage[a4paper, top=1.6cm, bottom=2.54cm, left=3.18cm, right=3.18cm, showframe]{geometry} % 调整上边距为2cm
\usepackage{amsmath}
\usepackage{tikz}
\usepackage{nicematrix}
\title{\kaishu 查漏补缺}
\author{\kaishu 制作人:xxx}
\date{\today}
\bibliographystyle{plain}
\begin{document}
\maketitle
\begin{center}
\textbf{\kaishu{认真就是水平, 扎实就是能力.}  }
\textbf{\kaishu{}}
\end{center}

\section*{\kaishu{薄弱点}}

\begin{tikzpicture}[overlay,remember picture]
\node[scale=.5] at ([yshift=2cm]current page.center) {$
    \begin{bNiceArray}{*6c*6c}[columns-width=2mm,margin]
        \Block[borders={bottom,right,tikz=dashed}]{6-6}<\LARGE>{\mathbf{E}_{6m}}&&& & & &\Block[borders={bottom,right,tikz=dashed}]{2-4}<\Large>{\mathbf{O}} & & & & \Block[borders={bottom,tikz=dashed}]{2-2}<\Large>{\mathbf{E}_{2m}}& \\
        & &&&& & & & & & & \\
        & &&&& &\Block[borders={bottom,right,tikz=dashed}]{4-4}<\Large>{E_{4m}} & & & &\Block[borders={bottom,tikz=dashed}]{4-2}<\Large>{\mathbf{O}} & \\
        & &&&& & & & & & & \\
        & &&&& & & & & & & \\
        & &&&& & & & & & & \\
        \Block[borders={bottom,right,tikz=dashed}]{5-1}<\Large>{\mathbf{O}} &\Block[borders={bottom,right,tikz=dashed}]{5-5}<\LARGE>{\mathbf{E}_{5m}}&& & & &\Block[borders={tikz=dashed}]{6-6}<\Large>{\mathbf{E}_{6m}} & & & & & \\
        & &&&& & & & & & & \\
        & &&&& & & & & & & \\
        & &&&& & & & & & & \\
        & &&&& & & & & & & \\
        \Block[borders={bottom,right,tikz=dashed}]{1-1}<\Large>{\mathbf{E}_{m}}&
        \Block[borders={bottom,right,tikz=dashed}]{1-5}<\Large>{\mathbf{O}} &&&& & & & & & & \\
    \end{bNiceArray}
$};
\end{tikzpicture}

\end{document} 

另外，那个多余的问题请删了吧，看着太难受了（呜呜呜呜）

好的好的，谢谢