It's not that Gnome can't, it's that it's not recommended. Gnome actually handles e.g. 150% scaling the exact same way as macOS does: render at a higher resolution then downscale. The reason it's not recommended over integer scales is that's inefficient, not that it doesn't work. The same recommendation exists on macOS. The difference in quality of life is macOS is generally better about assuming a given display should be high DPI the first time you use that display (and doesn't even show you the tiny options at all by default in such cases). So long as you select the same scale things should seem identical between Gnome and macOS though.

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).

> See but that's exactly the thing, on Mac you can just pick a scaling and every scaling option looks flawless across the board.

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.