Comment # 42 on bug 1089932 from Terje J. Hanssen

This is on Gnome DE:

cat /etc/sddm.conf
[XDisplay]
EnableHiDPI=true
# ServerArguments=-nolisten tcp -dpi 240


I hope the comment char # is correct.

Regarding your mentioned "something that scales up", I also see Gnome Settings
> Devices > Monitors show Built-in monitor 3840x2160 has Scale set to 200%


xrdb -remove
QT_AUTO_SCREEN_SCALE_FACTOR=1 sddm-greeter --test-mode --theme
/usr/share/sddm/themes/breeze-openSUSE
[15:03:34.635] (II) GREETER: High-DPI autoscaling Enabled
[15:03:34.775] (II) GREETER: Reading from
"/usr/share/xsessions/gnome-xorg.desktop"
[15:03:34.775] (II) GREETER: Reading from "/usr/share/xsessions/gnome.desktop"
[15:03:34.775] (II) GREETER: Reading from
"/usr/share/xsessions/icewm-session.desktop"
[15:03:34.776] (II) GREETER: Reading from "/usr/share/xsessions/icewm.desktop"
[15:03:34.776] (II) GREETER: Reading from
"/usr/share/xsessions/plasma5.desktop"
[15:03:34.776] (II) GREETER: Reading from "/usr/share/xsessions/twm.desktop"
[15:03:34.776] (II) GREETER: Reading from
"/usr/share/wayland-sessions/gnome.desktop"
[15:03:34.777] (II) GREETER: Reading from
"/usr/share/wayland-sessions/plasmawayland.desktop"
[15:03:34.778] (II) GREETER: Loading theme configuration from
"/usr/share/sddm/themes/breeze-openSUSE/theme.conf"
[15:03:34.783] (EE) GREETER: Socket error:  "QLocalSocket::connectToServer:
Invalid name"
[15:03:34.827] (II) GREETER: Loading
file:///usr/share/sddm/themes/breeze-openSUSE/Main.qml...
[15:03:34.867] (WW) GREETER: QObject: Cannot create children for a parent that
is in a different thread.
(Parent is QGuiApplication(0x7ffcf7e05a80), parent's thread is
QThread(0x55e5d27fc830), current thread is QThread(0x55e5d2a88db0)
[15:03:34.868] (WW) GREETER: QObject: Cannot create children for a parent that
is in a different thread.
(Parent is QGuiApplication(0x7ffcf7e05a80), parent's thread is
QThread(0x55e5d27fc830), current thread is QThread(0x55e5d2a88db0)
[15:03:34.868] (WW) GREETER: QObject: Cannot create children for a parent that
is in a different thread.
(Parent is QGuiApplication(0x7ffcf7e05a80), parent's thread is
QThread(0x55e5d27fc830), current thread is QThread(0x55e5d2a88db0)
[15:03:34.868] (WW) GREETER: QObject: Cannot create children for a parent that
is in a different thread.
(Parent is QGuiApplication(0x7ffcf7e05a80), parent's thread is
QThread(0x55e5d27fc830), current thread is QThread(0x55e5d2a88db0)
[15:03:34.868] (WW) GREETER: QObject::installEventFilter(): Cannot filter
events for objects in a different thread.
[15:03:34.869] (WW) GREETER: QObject: Cannot create children for a parent that
is in a different thread.
(Parent is QGuiApplication(0x7ffcf7e05a80), parent's thread is
QThread(0x55e5d27fc830), current thread is QThread(0x55e5d2a88db0)
[15:03:35.175] (WW) GREETER: QObject: Cannot create children for a parent that
is in a different thread.
(Parent is QGuiApplication(0x7ffcf7e05a80), parent's thread is
QThread(0x55e5d27fc830), current thread is QThread(0x55e5d2a88db0)
[15:03:35.175] (WW) GREETER: QObject::installEventFilter(): Cannot filter
events for objects in a different thread.
[15:03:35.391] (WW) GREETER:
file:///usr/share/sddm/themes/breeze-openSUSE/components/VirtualKeyboard.qml:20:1:
module "QtQuick.VirtualKeyboard" is not installed
[15:03:35.520] (II) GREETER: Adding view for "eDP-1" QRect(0,0 1280x720)