Something like this that's proven itself: https://www.figma.com/blog/webassembly-cut-figmas-load-time-...
TLDR: C++, WASM, and some form of GRPC with C++ on the server side as well. Because you need a language that's fast, can contain high complexity and large programs without collapsing (which is a short list of languages) and can work fast for the bits that need speed.
I’m my opinion, you have to be kinda masochist to choose C++ for this. Web development is hard in C++.
But thanks for answering honestly.
That article is seemingly all about the perf of the complex frontend app with a custom renderer running in the browser, nothing to do with what’s happening on the server.