How can I get an upright \hbar using unicode-math?

Question

I would like to have an upright \hbar glyph in my documents and I'm using unicode-math. The example in https://tex.stackexchange.com/a/527104/218142 doesn't seem to work when I load unicode-math. The bar obviously moves relative to the h. Why does this happen, and how can I get the upright \hbar when loading unicode-math?

My MWE:

% !TEX program = lualatexmk
% !TEX encoding = UTF-8 Unicode
\documentclass{article}
\usepackage{unicode-math}
\begin{document}
\renewcommand{\hbar}{{\mathpalette\hbaraux\relax\symup{h}}}
\newcommand{\hbaraux}[2]{\sbox0{\mathsurround=0pt$#1\mathchar"AF$}\mkern-1mu\lower.07\ht0\box0\mkern-8mu}
( \hbar \scriptstyle\hbar \scriptscriptstyle\hbar )
\end{document}

This MWE produces the following output:

Answer 1

You don't need to construct things by hand, you want U+0127 ħ

\documentclass{article}
\usepackage{unicode-math}
\begin{document}
\renewcommand*{\hbar}{\mathrm{^^^^0127}}
( \hbar \scriptstyle\hbar \scriptscriptstyle\hbar )
\end{document}

Answer 2

You can compose the character, but you have to do it the proper way:

\documentclass{article}
\usepackage{unicode-math}
\makeatletter
\AtBeginDocument{%
  \DeclareRobustCommand{\hbar}{{\mathpalette\hbar@\relax\symup{h}}}%
}
\newcommand*{\hbar@}[2]{%
  \makebox[0pt][l]{\raisebox{-0.07\height}{$\m@th#1\mkern-1mu\mathchar"AF$}}%
}
\makeatother
\begin{document}
( \hbar \scriptstyle\hbar \scriptscriptstyle\hbar )
\end{document}