Take a look at the picture below:

This is the Unicode I want to use!
PDF address: https://www.unicode.org/charts/PDF/U1D400.pdf
Take a look at the picture below:

This is the Unicode I want to use!
PDF address: https://www.unicode.org/charts/PDF/U1D400.pdf
Using unicode-math (and luatex or xetex) you can use Unicode input or more classical ascii command forms, for the same output.
\documentclass{article}
\usepackage{unicode-math}
\showoutput
\begin{document}
$ = ²$, $$
$E=mc^2$, $\symbf{\theta}$
\end{document}
expl3loop found at the end of this answer: https://tex.stackexchange.com/a/201248 – Niranjan Dec 28 '22 at 07:21