Try the KDE applications designed for this, like kasts, alligator, qrca and see for yourself.

I don't think it can necessarily work for any kind of application, but for some simpler ones I think it's completely fine.

> designed for this

This is kind of my point - I'm not saying you can't have applications that are usable across multiple UX paradigms, and I'm also not saying you can't write a UX library that automatically translates at least simple applications with little manual effort.

I'm just saying this requires active buy in from application developers into the ecosystem - you can't just run everything on all devices and have it magically work (with usability comparable to current state of the art in single device applications).

And to have buy in it needs to exist first :)

Like websites nowadays being usually designed for mobile and desktop devices

kirigami

> I'm just saying this requires active buy in from application developers into the ecosystem

It's true, but on the other hand, it's much easier to adapt your desktop app to a smaller screen than to rewrite it completely for another OS.