Wasm is not just bleeding edge, it is supported by all major browsers and being used in all sorts of real-world websites. No, "Qt" is not the only way to do UI in C++/wasm. This is a basic misunderstanding of the technology. Wasm lives inside the Javascript vm and can manipulate DOM objects all day long. It's just not very practical to do so. There are plenty of Rust projects going in that direction, though...
C++ doesn't only require you to be precise, it requires you to be verbose. JS is quite precise, and a lot more expressive because of the runtime. TypeScript is all of this and also allows you to be more explicit in order for the compiler to check your work, much like a proof checker.
The C++ type system is relatively stupid compared to that of TypeScript and F#, for example. In TS and F#, you can use types to help you, in C++ you already need the types because otherwise the compiler doesn't have a clue what to do.
