KDE will have working fractional scaling for the DE and apps using QT and there you can adjust a slider to a % you like.
Integer scaling is silly for me: it's either huge or tiny.
Yes, KDE does it better and with Wayland you can also do fractional scaling. But the original point stands: it sucks on (most) linux and works flawlessly on Mac.
Windows/Android also use the superior direct render approach. The reason you always heard about Windows having horrible scaling was due to legacy Windows apps not having an understanding of how to use scaling, the actual scaling approach itself is very good (and most all apps still getting updates should be good by now).
Not really, if you have a discerning eye.
Any non-integer resolution on macOS is rendered at twice that resolution, and then raster-scaled down and anti-aliased. So, if you have MacBook with a 2560×1400 display and you select any other resolution besides that and 1280×800 (exactly half), the desktop render will be raster scaled.
To be fair, it works better than Wayland's previous behaviour because of the 2× rendering factor, but you can absolutely still see scaling artifacts if you look for them, and I certainly do. Ringing around text in a dark-mode editor is especially obvious.
The only OS that has gotten HiDPI right is Windows.
On Linux, I plugged in the 4k and everything is tiny tiny tiny. I tried to make it a little bigger, and some stuff grows, other stuff doesn't, and some stuff just broke. Then in the end I was sort of stuck in this weird frankenstein of settings that looked like crap on any monitor. Like I said, this was over 3 years ago and the Linux install was very old at that point (I think it was a Linux Mint based on 18.04 at the latest, possibly even 16.04 still).
Mac has a slider that changes the scaling of everything, smoothly and all at once.
I probably should have just gotten a bigger 4k