xsettingsd is pulled in by kde-gtk-config and also started automatically in a KDE Plasma X11 session. When changing global scaling in display configuration of kde systemsettings the daemon will take care of setting the font scaling for GTK apps like Steam.
While xsettingsd works for X11 it doesn't for wayland. org.gnome.desktop.interface text-scaling-factor can be used instead.
$ gsettings get org.gnome.desktop.interface text-scaling-factor
1.0
$ gsettings set org.gnome.desktop.interface text-scaling-factor 1.25
This however also affects other applications like Firefox, so having Steam scaled bigger would also scale other applications. A workaround to this is setting an environment variable for Steam manually via e.g. .bash_profile.
$ nano -w ~/.bash_profile
# gsettings get org.gnome.desktop.interface text-scaling-factor
# 1.0 but we want just steam bigger else it also affects firefox
# and other GTK applications.
export STEAM_FORCE_DESKTOPUI_SCALING=1.25