Upright greek letters in math mode

Hi!

I use MathJax plugin for my WP site. My content is mostly math related and therefore I often use units (such as micrometer, μm).

Problem is that greek letters are italicized by default, and using \mathrm{} does not make them upright as it does with latin letters.

In LaTex one can include packages that fix this problem (such as isomath, upgreek), but for my understanding, it is not possible to include packages in MathJax.

But I found some advice on this page, saying (quote)

“This package is not autoloaded, so you must request it explicitly if you want to use it. To load the upgreek extension, add ‘[tex]/upgreek’ to the load array of the loader block of your MathJax configuration, and add ‘upgreek’ to the packages array of the tex block.”

So, I tried searching through my setting, but I have no idea what “load array of the loader block of your MathJax configuration” is, and is it possible to include a package to MathJax that way?

Can someone help me with this:
1. is the advice from this page applicable and will it solve the greek upright problem? (if not – what will?)
2. where do I load this exactly; where can I find the load array of the loader block?

Thank you!