Sorry if off-topic, but is it possible to create native cross-platform apps that look like this without using electron & co?
I've played around with Qt, and the applications just don't look that good to me. And flutter for Desktop, while promising, just looks like mobile apps on desktop.
Vanilla Qt (no QML) supports a decent subset of CSS(QSS) that can target widgets and objects etc. It's quite a bit of work if you're just getting started but it just comes down to knowing what to override, disable and what can be styled etc. In extreme cases where the native widgets are limiting you can just draw your own. I believe you could recreate about any interface with just Qt.
Three random apps of mine that use Qt and all look different but if you grok the src you can get an idea of what I mean.
1. https://github.com/iKlsR/Markr (https://github.com/iKlsR/Markr/blob/main/src/res/style.qss)
2. https://github.com/iKlsR/Playground
3. https://github.com/iKlsR/SDFSandbox (This one uses custom drawing for the node widgets)
It's probably Material Design "looks like mobile apps" on desktop, not Flutter itself.
Flutter gives you all the tools and flexibility to style and design your app as you wish. I'm developing Desktop apps in Flutter for 2 years now and I think it's the best thing that happened to desktop UI development since Qt in early 2000.