The following code:

\documentclass{article}
  
\begin{document}
\[ f(x',\overline{x'}) \]
\end{document}

produces the following output for me:

I'm a bit bothered that the heights of the primes are mismatched. My first thought for how to fix this issue was to add a phantom overline over the first argument so that the prime in the first argument would get pushed down to the same height. However, despite some experimentation with syntax (\phantom{\overline}{x'} for instance), I couldn't find something which compiles.

Apologies if this has been asked before. The inverted version of this question overline over no text does not seem relevant here.