It's on the road to improve, as GNOME continues work here. KDE users have reported a cleaner look overall for applications that are not displaying in a way folks would like to see. Fedora Workstation for example, keeps folks to a 100 or 200% scale due to this, but it can be enabled easily enough if on e prefers.
This is an area of active development that will continue to see improvement.
Note GTK3/4 doesn't have true fractional scaling. What it does is scaling up to 2x and downsample to the required resolution. This is not that visible but it does produce some blur, along with the performance overhead. Qt5 doesn't support it either, though Qt6 does. Of course we'll see improvement, but I doubt it would get to the same level as Windows in the next 5 years or so, which is a long time.
125% and 150% are really common for available laptops though. The former for the 1920x1200 13-14 inch laptops, the latter for 2560x1600 15-16 inch laptops. iOS doesn't do fractionally scaling, only 2x, and Macs are all designed to run at 200%, though you can set it to 175% or 150%. MacOS looks equally terrible at 125% or 100% (this is due to the lack of subpixel rendering, but I digress)
Oh, it does. The framebuffer is integer scaled, but the physical display has different (lower) resolution. As I wrote above, this mismatch is handled by the output encoder.
> Macs are all designed to run at 200%, though you can set it to 175% or 150%.
Macs since around 2016 ship with ~175% default.
Again, the framebuffer is integer scaled (make a screenshot and see for yourself), and then fit to the display with lower resolution.
They do not support 150% or 175% though; these numbers are never shown in UI, just some description like "more space". This is not just Apple-esque hiding of everything that might sound technical; they really do not support 150% or 175%. In reality, it is more like 177,78% or 152,38%; they get something out of it, but that is a different topic.
It is exactly the same approach that Gnome / Mutter uses for fractional scaling. Except that Mutter did the mistake with exact scales.
Oh, iPhones do fractional scaling now, and have for years. The display has gotten much more pixel dense. It is not reported to the developer or the user what the real resolution is.
This is an area of active development that will continue to see improvement.