Hi! Thanks for your review :)

Unfortunately Gemini uses KaTeX but does not store the LaTeX code anywhere, usually it is stored inside a katex-mathml (in the 'annotations' tag) which is sibling to the generated katex-html. You can check yourself with F12 or Ctrl+Shift+C that there is no LaTeX code in the HTML of the page.

With MathJax this can be solved via the MathJax API because it internally stores MathItems in the DOM that contain a lot of information (including their latex code) but KaTeX does not store this DOM math elements, it only renders the HTML.

So long story until Gemini improves it's KaTeX rendering to the standard (that also includes an annotations tag with the LaTeX code) this extension (or any extension really) won't be able to copy mathematical expressions from Gemini.