There are two different things mixed together: - fractional scaling of the display output - app rendering at fractional scales. The first one works fine with

There are two different things mixed together: - fractional scaling of the display output - app rendering at fractional scales. The first one works fine with Gtk 3 and newer; the application renders its output at nearest higher integer scale, and then the compositor downscales it to requested fractional scale (i.e. app renders at 200% and compositor downscales it to 175%). Apple does exactly this same thing (just with slightly different scales; they won't show you nice 150% or 175% for a reason; they optimize for different thing). The second one is rendering at fractional scales directly by the application; then the compositor doesn't downscale anything, just displays the buffer as it is (i.e. app renders at 175% and compositor displays it as it is). Since rendering at fractional scales is more demanding (just think about fractional mouse coordinates or how to display 1px straight line and don't get lost in the rounding errors), it took longer to materialize. It is this support that will have to wait for Gtk 5. But meanwhile, your (Gtk) apps will be displayed at fractional sizes using the first method.