For UI I do think JS is your best option atm. You don't have to write JS to generate JS, you can use Typescript or go more exotic to things like Rescript.

In terms of CSS; you'll need some form of styling in whatever language, there are plenty of abstractions on top of CSS if you want [something not css].

I would suggest having a look at Next.js if a web app would work, React Native (use Expo) if you want mobile, or Tauri if you want to focus on desktop (Electron, but in Rust, more performant, smaller size, more secure).

Another thing worth checking out is Flutter. I'm personally not a huge fan for irrelevant reasons but it is cross platform, and it's compiled not-JS (Dart).

I also want to say FE has come a long way, the web platform is much more stable, there are great frameworks and libraries, the tooling is amazing, and above all it's really fun and productive. Give it a shot, you might enjoy it. (Do use TS, or Rescript, or something, JS is better with types).