Bolding text generated by physics package

I would like to point out that you can change the font of \partial and d with the derivative package using the option style-inf=<font>

\documentclass{article}

\usepackage{amsmath}
\usepackage{bm} % pdflatex

%\usepackage{unicode-math} % lualatex or xelatex

\usepackage{derivative}

\derivset{\pdv}[style-inf=\bm]  % pdflatex
\derivset{\odv}[style-inf=\bm]  % pdflatex
%\derivset{\pdv}[style-inf=\symbf]  % lualatex or xelatex
%\derivset{\odv}[style-inf=\symbf]  % lualatex or xelatex

\begin{document}
    \begin{equation}
        \pdv{ f(x,y,z) }{ x, y, z } \quad \odv{ f(x) }{ x }
    \end{equation}
\end{document}

If you want upright bold d, then you should use \RenewOdvVariant{\odv}{\bm{\mathrm{d}}} with pdflatex instead of \derivvset, because \derivset{\odv}[style-inf=\bm\mathrm] will throw an error.

The diffcoeff package also allows the easy use of a bold \partial or d. You will need names for them, say ob for ordinary-derivative-bold, and pb for partial-derivative-bold:

\documentclass{article}
\usepackage{bm}
\usepackage{diffcoeff}
\diffdef{ob}{ op-symbol = \bm{ \mathrm{d}} }
\diffdef{pb}{ op-symbol = \bm{\partial} }
\begin{document}
\[
\diff.ob.{\mathcal{Q}(\bm{\tau})}{\tau_{t}}\qquad
\diff.pb.{\mathcal{Q}(\bm{\tau})}{\tau_{t}}
\]
\end{document}

If you don't want to write \diff.ob. and \diff.pb. all the time, follow the \diffdef commands in the preamble with

\newcommand{\ob}{\diff.ob.}
\newcommand{\pb}{\diff.pb.}

or some other names of your choosing. You can then replace the \diff.ob. with \ob and \diff.pb. with \pb.

I will use the classic \frac instead of the packages physics, diffcoeff, derivative.

\documentclass[a4paper,12pt]{beamer}
\usepackage{mathtools,amssymb}
\usepackage{bm}

\begin{document}
\[
  \mathcal{Q}(\bm{\tau})=\frac{{\bm\partial}z^*(w)}{{\bm\partial}\tau_t}\frac{{\bm d}x}{{\bm d}t}
\]
\end{document}