\begin{table}
\centering
\begin{tblr}[         %% tabularray outer open
]                     %% tabularray outer close
{                     %% tabularray inner open
colspec={Q[]Q[]Q[]Q[]},
hline{2}={1,4}{solid, black, 0.05em},
hline{3}={1-4}{solid, black, 0.05em},
hline{2}={3}{solid, black, 0.05em, l=-0.5},
hline{2}={2}{solid, black, 0.05em, r=-0.5},
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cell{3,5}{1}={}{font=\bfseries},
cell{4}{1}={c=4}{font=\bfseries},
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foo &  & bar &  \\
mpg & cyl & disp & hp \\
21.000 & 6 & 160 & 110 \\
hello world & hello world & hello world & hello world \\
21.000 & 6 & 160 & 110 \\
22.800 & 4 & 108 & 93 \\
21.400 & 6 & 258 & 110 \\
\end{tblr}
\end{table} 
