\documentclass[border=3mm, tikz]{standalone}

\usepackage{pgfplots}
\usepackage{xcolor}

\usepackage[utf8x]{inputenc}
\usepackage[greek,english]{babel}

\definecolor{Beize}{HTML}{e6d397}

\usepackage{tabularray}

\begin{document}
\begin{tikzpicture}
\node[anchor=north,scale=0.4] at (2.75, 0.2) {
$M(R) = \quad $\begin{tblr}{
  rows = {1.5em, rowsep = 2pt},
  columns = {1.5em, colsep = 2pt},
  cells = {m,c},
  hlines = {1pt},
  vlines = {1pt},
  cell{1}{2} = {Beize},
  cell{1}{3} = {Beize},
  cell{1}{4} = {Beize},
  cell{1}{5} = {Beize},
  cell{2}{1} = {Beize},
  cell{2}{3} = {Beize},
  cell{2}{4} = {Beize},
  cell{2}{5} = {Beize},
  cell{3}{1} = {Beize},
  cell{3}{2} = {Beize},
  cell{3}{4} = {Beize},
  cell{3}{5} = {Beize},
  cell{4}{1} = {Beize},
  cell{4}{2} = {Beize},
  cell{4}{3} = {Beize},
  cell{4}{5} = {Beize},
  cell{5}{1} = {Beize},
  cell{5}{2} = {Beize},
  cell{5}{3} = {Beize},
  cell{5}{4} = {Beize},
}
1 &  &  &  &  \\
 & 1 &  &  &  \\ 
 &  & 1 &  &  \\ 
 &  &  & 1 &  \\ 
 &  &  &  & 1 \\ 
\end{tblr}
};

\end{tikzpicture}
\end{document}