Outside of deeply integrated KDE apps, I'm shipping QML + Python apps and IMO it's a nice experience.

It's not at all like you're writing JS apps a la React or jQuery, JS syntax is used for expression eval at minimum, but you don't have to use it beyond some single handlers, formatting/convenience functions, or whatever.

I'm looking at a smaller app, with 5k lines of QML and 10k of Python. It's got 250 lines of JS according to tokei, and quickly poking at the QML for JS leads to an additional 200 lines, so let's double to 500 lines. That's like 3% JavaScript.

That said, modern KDE is centered around QML, UI frameworks like Kirigami are built using it, but it lacks comprehensive QML, Python, Rust, etc bindings for KDE frameworks.

At minimum, you will at some point be reading C++ docs and to use your bindings. If you get in the weeds with it, you will be writing your own bindings or wrappers eventually. If you want to avoid that, you will likely be writing C++ for more complicated applications.

It's complex, but I figured with QML Plasmoids they were going for a QML-first approach to future development, but that's been walked back in favor of compiled Plasmoids in recent releases.