This question is more specific to MathJax than to Obsidian, but nonetheless I’ve done a little bit of research and as far as I can tell this isn’t currently supported.
- MathJax out of the box only supports symbols that are contained in the
\oiiint are contained in the following packages (but not in
- MathJax support a series of extensions to enrich its features.
But currently Obsidian doesn’t support MathJax extensions.
- But currently Obsidian doesn’t support a MathJax extension that contians that symbol (extension/package that currently might not exist at all)
There are a bunch of threads here on the forum about MathJax extensions support, maybe you can bump them to keep the request alive.