For tech, I'd consider both Cocoa + Swift and SwiftUI as candidates for UI components, on a case-by-case basis. Swift is not my favorite language (feels like I have to use Xcode; have yet to try out the JetBrains IDE), but it gets the results I want. Perhaps in the future, we can use Rust in a more ergonomic fashion to talk with native UIs.
Honestly, I'd love an ObjC-like language that interops with ObjC and has strong static typing with a dynamic typing escape hatch for metaprogramming.
The FOX codebase isn't terribly modern, as it's older than the standard C++ concurrency machinery, but it works.
It depends on the target market for your application I suppose - if your target won't be happy unless they have html/CSS or similar animations, then using something with low latency isn't going to make them happy.
Personally I don't mind the Windows 98 look, it strikes me as clean and no-nonsense. Everything is clear and high-contrast. Unlike with many 'flat' themes, it's generally clear what's clickable. I realise not everyone likes the Windows 98 look though.
If someone is serious about developing fast GUI apps, trading off on themeability is the kind of thing they should consider. As you say, FOX really is fast. I presume this is because of its uncompromising hard-coded native-code-only approach - it's just a C++ codebase. All the drawing operations are implemented directly in C++. Unlike Qt, there's no JavaScript. Unlike JavaFX, there's no CSS. It's all just C++.
Perhaps a GUI toolkit could add themeability without any performance impact by implementing it as a compile-time abstraction.
> depends on the target market for your application I suppose - if your target won't be happy unless they have html/CSS or similar animations, then using something with low latency isn't going to make them happy
Right, but mattgreenrocks said fast, focused, and respect the user's time and computing resources, presumably in contrast to current norms.