Bold math does not seem to work on the desktop Anki version, at least not on the linux client, but does work in AnkiDroid. For instance, the MathJax line
(x = \boldsymbol{x} = \mathbf{x} = \mathrm{x})
Produces
on my desktop client but should produce (from MathOverflow)
Maybe youāre not using the latest Anki version (2.1.35). Iām on Windows and it works for me, but I just checked Linux installation file and boldsymbol.js can be found in bin\aqt_data\web\mathjax\extensions\TeX.
And if I use AnkiWebView Inspector add-on, the bold symbol has been rendered with MathJax_Math font and font-family: MJXc-TeX-math-BI,MJXc-TeX-math-BIx,MJXc-TeX-math-BIw.
I donāt know if it means something or not, but if I set the env var QTWEBENGINE_REMOTE_DEBUGGING to 8080 prior to starting Anki (https://addon-docs.ankiweb.net/#/porting2.0?id=webview-changes), open localhost:8080 and navigate to Application tab, I can see MathJax_Main-Bold.woff in Fonts.
Well, thatās strange. I donāt even have a āfontsā category. I only have a āscriptsā category with MathJax.js, Math-BoldItalic.js, and MathEvents.js (plus a bunch of other stuff).
I just tested it on Ubuntu 20.04 (running in VirtualBox), and bold font doesnāt seem to be rendered properly for me either. Apparently 4 font files (.woff) are loaded in Anki windows version, but not in Ubuntu.
on Windows (anki-2.1.36beta1-53a984ba-windows.exe):
I experience the same problem, also using Ubuntu and latest Anki version. Iām pretty sure I had it since Iāve started using desktop Anki a bunch of years ago
Good news here, in the next version of Anki 2.1.36, there will be a lot of improvements to MathJax.
One improvement is that we updated to MathJax 3, but the Anki MathJax will also include more functionality, which includes purposefully or autoloading extensions. So in the future, you can simple use \require{boldsymbol} to load the boldsymbol extension, after which the example in the opening thread should render like you wanted.