It’s all widgets, no canvas. If you made it in any of the above it won’t feel Spotify it’ll feel Qt or whatnot. For Linux and FOSS types this is usually fine. It’s sure fine for me. But for the vast majority of users it isn’t.
And I don’t think anyone wants to write the application natively thrice.
When it comes to “mostly canvas” applications I find myself thinking about using game engines. They’re portable and basically that: a canvas with some basic UI support.
This is not hard to imagine since various UI frameworks have long had issues with different paste board systems on Linux.
That's a bug.
> various UI frameworks have long had issues with different paste board systems on Linux
In my experience on *nix (37 years, going back to SunOS), the paste board systems for X Window are very well defined, and the only UI frameworks that have "long had issues" with them are buggy and not widely used. Are you thinking of something in particular?
There's still issues today on Linux with keyboard shortcuts. Some apps use Ctrl+Shift and others use only Ctrl, there's no way to know what an app uses a priori. You have to hope the shortcut is displayed in the menu and you remember it when you need to actually use it. Different frameworks have different default shortcuts for common behaviors. Accessibility for any individual app is still hit or miss, same with localization and theming. Mac and Windows users don't face anywhere near the same impedance mismatch between various first and third party applications. Those systems are far from perfect but they're usually much more consistent UX than a Linux desktop.
This leaves several notable areas of UI/UX to address:
1. menus 2. file browsers 3. text entry 4. notification/tray integration 5. window management
These are where "the native experience" (i.e behaving according to guidelines or rules laid down by the platform controller) is really felt.
Yet they have very little to do with the "interior" (in-window) behavior of the app at all, despite being critically important.
If we're going to continue with the construction metaphor, I'd say it's more like creating a lovely house that has unusual door handles, windows that open in strange ways, and a different LED lighting temperature than you're used to.