Falling down the rabbit hole of HiDPI screens and fractional scaling on Linux desktops I came across an interesting discussion on Reddit. It contains a lot of useful links that help to form an opinion on the subject.
I found that in the KDE X11 session fractional scaling is implemented on Qt Framework level, so each app scales its output itself. Gnome uses a different technique. It implies rendering everything at an integer factor and then downscaling using a raster operation. It’s a more universal approach and does not depend on the GUI framework, but it can lead to some sort of degradation for the font rendering. It can be almost invisible for Apple-like retina displays with a 1.75 scale factor but it’s notable on the average 13" - 14" laptop 1080p screen.
I think the best way to avoid HiDPI rendering issues is using such displays that allow setting integer scale factors like x2 on a 14" screen with 2880х1800 resolution. All other techniques will be always the compromise between GUI framework requirements, multi-screen setup support, performance, and final picture quality.