The experimental fractional scaling that GNOME provides is nice but only works w/ apps that have been ported to Wayland. Everything that runs in XWayland (Firefox, Thunderbird, emacs) shows up as extremely blurry.
I've got the exact same 1440p screen as you on my Thinkpad (which wants to be run at 1.5x or 1.75x) and the best solution I've found is provided by KDE. Try installing Plasma (either by installing Kubuntu or just installing the desktop w/ apt) and setting Display->Scaling to 2X and then go into fonts separately and set "force font DPI" to 168. That's working remarkably well for both GTK and QT apps for me. 2X scaling for windows/icons keeps them from being tiny/blurry and setting the font size to 168 (aka 175%) prevents the fonts from being huge.
I've got the exact same 1440p screen as you on my Thinkpad (which wants to be run at 1.5x or 1.75x) and the best solution I've found is provided by KDE. Try installing Plasma (either by installing Kubuntu or just installing the desktop w/ apt) and setting Display->Scaling to 2X and then go into fonts separately and set "force font DPI" to 168. That's working remarkably well for both GTK and QT apps for me. 2X scaling for windows/icons keeps them from being tiny/blurry and setting the font size to 168 (aka 175%) prevents the fonts from being huge.