Hey, thanks for adding to the thread.
The native Preview | Markdown and the WYSIWYG editor in general still doesn’t render math. KaTeX via $...$ or $$...$$ isn’t supported there yet. It uses a separate renderer from the classic preview, so the classic one works. We know about this issue and we’re tracking it, but I can’t share an ETA yet.
Workaround on desktop: open the .md file in Text Editor, then run Markdown: Open Preview to the Side with Cmd+Shift+V. $ and $$ will render correctly via KaTeX there.
About the iOS app, that’s a separate surface owned by another team. It’s best to keep the discussion in the thread you linked iOS app not rendering LateX so the report lands in the right queue. We’re tracking that too, but no ETA.
Let me know if the classic preview workaround doesn’t fit your use case.