It seems I’ve figured it out after reading this post: SDDM doesn't load unless external monitor plugged in - #6 by tachyon! Here is my new ‘/etc/X11/xorg.conf,’ which might be useful in case someone finds themselves in a similar situation to mine:
# nvidia-xconfig: X configuration file generated by nvidia-xconfig
# nvidia-xconfig: version 545.29.06
Section "ServerLayout"
Identifier "Layout0"
Screen 0 "Screen0"
InputDevice "Keyboard0" "CoreKeyboard"
InputDevice "Mouse0" "CorePointer"
EndSection
Section "Files"
EndSection
Section "InputDevice"
# generated from default
Identifier "Mouse0"
Driver "mouse"
Option "Protocol" "auto"
Option "Device" "/dev/psaux"
Option "Emulate3Buttons" "no"
Option "ZAxisMapping" "4 5"
EndSection
Section "InputDevice"
# generated from default
Identifier "Keyboard0"
Driver "kbd"
EndSection
Section "Monitor"
Identifier "Monitor0"
VendorName "Unknown"
ModelName "Unknown"
Option "DPMS"
EndSection
Section "Device"
Identifier "Device0"
Driver "nvidia"
VendorName "NVIDIA Corporation"
Option "AllowEmptyInitialConfiguration"
BusID "PCI:1:0:0"
EndSection
Section "Device"
Identifier "iGPU"
VendorName "Intel Corporation"
Driver "modesetting"
BusID "PCI:0:2:0"
EndSection
Section "Screen"
Identifier "Screen0"
Device "iGPU"
Monitor "Monitor0"
DefaultDepth 24
Option "AllowEmptyInitialConfiguration" "True"
SubSection "Display"
Depth 24
EndSubSection
EndSection