FWIW, I tried adding the directives to /etc/sddm
$ cat /etc/sddm.conf
[X11]
ServerArguments=-nolisten tcp -dpi 96
But things didn’t get fixed until I updated my nvidia drivers which are now at
aur/nvidia-390xx-utils 390.144-3 (+33 1.99) (Installed)
aur/nvidia-390xx-dkms 390.144-3 (+33 1.99) (Installed)
aur/nvidia-390xx 390.144-1 (+53 0.10)
I am using a rather ancient graphics card
$ inxi -G
Graphics: Device-1: NVIDIA GF108 [GeForce GT 630] driver: nvidia v: 390.144
Display: x11 server: X.Org 1.21.1.1 driver: loaded: nvidia unloaded: fbdev,modesetting,vesa resolution:
1: 1920x1080~60Hz 2: 2048x1080~60Hz
Message: Unable to show advanced data. Required tool glxinfo missing.