# \left ... \right make different sizes in numerator and denominator

the denominator is set in "cramped" style in which the exponent is lower, which has an effect on the left-right size, it is often best to use manual size `\left\right`

has an adverse effect on horizontal spacing, even when it does not stretch the delimiters.
here you could use `\bigl\|`

or simply `\|`

I simply add a response to generate brackets of the same size. I hope my code is clear. If there are some comments I am available.

```
\documentclass[a4paper,12pt]{article}
\usepackage{mathtools}
\DeclarePairedDelimiter{\norm}{\lVert}{\rVert}
\begin{document}
\[\frac{\norm{A^{-1}}}{\norm{A^{-1}}}\]
\end{document}
```