I'm a backend engineer and find the frontend tedious. I'd like to find something like latex, but that is also can scale nicely between PC and mobile screens.
Is this it? Anyone knows of a frontend solution that could support this use-case?
There are efforts for web maths, which would close the gap considerably for rendering science articles.
Most of the other LaTeX features can be achieved with HTML, CSS and maybe JS. Or even Markdown + preprocessor.
You are asking for a responsive weblayout, which excludes any format that LaTeX outputs. Latex is a typesetting engine that does the job before presenting anything and not while presenting it. Its layouts are not responsive by design.
So your question if there is something like LaTeX for frontend is just misplaced, because the working method of LaTex does not fit into a responsive weblayout frontend. What LaTeX features do you want in a frontend? How do you want to write code and how do you want the layout to happen?
What you describe sounds more like static site generation with math handling and perhaps references. There are markdown extensions that can handle such things. For rendering there is e.g. https://www.mathjax.org/