How to Add another language for highlighted code blocks

After some more digging I found this post:

In essence, it says that syntax highlighting in live preview is done by Codemirror 6, whilst syntax highlighting in the reader is done by primsJs. And they don’t necessarily support the same languages, and it’s not easy to get to them support the same languages.

So for syntax highlighting (for “iects”) to work in live preview, someone needs to extend the language support within Codemirror 6.