On Linux, it just depends on your desktop environment.

If you use KDE or any other Qt based one, HiDPI works perfectly at any scale, even in heterogenous environments – a landscape 4K 144ppi and a portrait 70ppi monitor right next to each other will work fine, and when moving applications they automatically rescale. On X11 and Wayland. The scale is set via the environmental variable

    QT_SCREEN_SCALE_FACTORS=DisplayPort-2=1.61;HDMI-A-0=1.08;

It’s GNOME and GTK which have almost no HiDPI support at all – they only support 96 and 192dpi (only integer scaling), and just added a feature for all other resolutions to just scale the windows down with blur. GTK2 still supported proper HiDPI, but with GTK3 they decided to abandon that and instead build apps that rely on pixels always being the same size. Considering how young GTK3 is this decision may sound a bit short-sighted, but the GNOME devs always refer to macOS as an example where this worked (while ignoring Android and Windows 10, which use fractional scaling, and ignoring the fact that with Gnome’s solution a game such as Minecraft on a 4K 144dpi screen is rendered at 6K and then half the resolution gets thrown away during the downscaling, because there is no option to avoid this)

The result is obviously completely broken.