Same, 2560x1440@14" scaling at 1.6.
Numix window decorations scale (where Arc doesn't) - I use Numix anyway so it works out, can't wait for proper fractional scaling since I'm a cinnamon user we'l likely get it around the same time.
Qt works fine for me. Have you set your Xft DPI?
$ cat .Xresources
Xft.dpi: 144
Xft.hinting: 1
Xft.hintstyle: hintslight
Xft.antialias: 1
Xft.rgba: none
Xcursor.size: 48
Xcursor.theme: AdwaitaThanks lima. .Xresources does not work on Wayland. In my case Qt apps work ok until I connect an external display. Here's before/after: https://imgur.com/a/bJb0J
Fractional scaling on 3.28 will allow you to have different scaling for each display. Will also be more consistent across different apps (Gtk, Qt, electron, etc.).