I spend all day with Firefox, terminals, and emacs in XMonad and they all scale perfectly with no raster UI elements. (XMonad's pixel boarder I didn't bother to scale.)
On Windows and MacOS last I checked, there was a lot more resized raster bullshit.
[1] https://www.linuxuprising.com/2019/04/how-to-enable-hidpi-fr...
You'll have to relog for the scaling to take effect with custom numbers for some reason
For my set-up at home (1080 - 4k - 1080) I have a simple script, that really was more of a `write once - use always`-experience. E.g.
xrandr --output HDMI1 --auto --scale 2x2 --pos 0x0+0+0
xrandr --output eDP1 --auto --scale 2x2 --pos 7680x0+0+0
xrandr --output DP1 --auto --mode 3840x2160 --scale 1x1 --pos 3840x0+0+0 --primary
Just a quick calculation in a repl, then called xrandr with the right scaling number, and presto, I had them exactly the same.
Then, with precise lining up of the displays, it was basically one seamless "sheet of paper". If I had a long web page or pdf spanning the displays (the laptop was directly under the monitors), then scrolling through it was quite "trippy".
I think because this was now a unified display where the bottom 1/3 was tilted differently to the top 2/3'rds (think of a curved ultrawide, but in portrait mode)
Honestly, it really was that simple.