125%, 150%, 175% - they’re all available out of the box on Windows 10, without even selecting a custom dpi.

Now try using them any of them, and you'll see what the GP meant. For example, try opening the (built in) device manager.

It's "good enough", honestly. It will never work perfectly with older apps, which is why Windows has started to default to just bitmap-upscaling them wholesale instead in many cases. And there are still nooks and crannies in Windows itself that are not high-DPI aware (another one is the font installer). But for day to day use, it's not something that you notice.

On Mac I used switchresx to add a new scaled resolution like this:

2560x1440 (native) * 1.5 = 3840x2160 HiDPI / 2 = 1920x1080 (effective resolution)

Obviously it is not as good a real panel but looked good enough to me.

I did the same thing on Ubuntu using xrandr, it was pretty good when it worked (sometimes it didn't, even using the exact same command)