For the ITS theme callouts infobox does anyone know how to do internal links?

I know that sounds were, but I’m trying to use this set up for the ITS theme callouts infobox, [[internal link|alt text]]. However, it breaks it and doesn’t render it. Just the text, ignoring the []. So does anyone else know some kind of trick to use the alt text?

As a reminder, these are for internal links, not external.

Agreed, alt text should work everywhere.
Try to contact the author of the ITS theme on GitHub to fix this issue for the benefit of everyone.