It possible to have subscript and super script that does not shrink the font size?

If you want this behavior everywhere:

\documentclass{article}

\DeclareMathSizes{10}{10}{10}{10}

\begin{document}
$a_{b_{c}}\quad x^{x^{x}}$
\end{document}

enter image description here

If it's just the one-off case, you can

\[ x^x x^{\displaystyle x} \]

enter image description here

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