Not until extremely recently[1] for fractional scaling. In my books, this is non-working HiDPI, because on Windows, my 15.6-inch full-HD notebook display is at 1.25× scaling, and my 27-inch UHD monitor is at 1.75× scaling. And since this is so recent, most DEs don't have support for this yet.
I was using mixed-DPI set-ups with no fanfare with Windows 8, 11 years ago. And Windows had initial HiDPI support with Windows 7.
I used to do this on Windows and found a ton of apps either broke their layout or got blurry when moved between monitors, so I wouldn't class Windows as 'ideal' here either :/
Not only moving the app itself between monitors. I fairly regularly get mis-scaled icons in the task bar when I've unplugged my laptop from its screen while it's closed.
I have yet to figure out how to get QT apps (and FreeCAD is particularly awful here) how to play well - there's always something scaled wrong no matter what I do.
I was using mixed-DPI set-ups with no fanfare with Windows 8, 11 years ago. And Windows had initial HiDPI support with Windows 7.
[1]: https://gitlab.freedesktop.org/wayland/wayland-protocols/-/m...