This wouldn’t be the *best* choice for doing more nuanced layout, say cutouts and things like that. But this has a ton of potential for repeatable design.
Tool is commercial, markup language is open-source.
The tool I used for this is called Typesetter, which is a Linux app on Flathub. Kind of impressed.
I feel like that split layout style that the markdown editor Mou originated in the early 2010s has proven super-influential even if Mou itself is forgotten.
@ernie i had a pretty good time using it for slideshows with the touying plugin
https://touying-typ.github.io/docs/intro
being able to export my slides as html is damn helpful. dont have to worry about having that specific presentation software on the end machine or lag or whatever.

Touying is a slide/presentation package developed for Typst. Touying is similar to LaTeX Beamer but benefits from Typst, providing faster rendering speed and a more concise syntax. After, we use "slides" to refer to slideshows, "slide" for a single slide, and "subslide" for a sub-slide.