How to force hiDPI scaling mode on boot in Pop!_OS/Gnome

Since your are using gdm, this should work for you system-wide:

1) Open the configuration file:

sudo nano /usr/share/glib-2.0/schemas/org.gnome.desktop.interface.gschema.xml

2) Change the default value to the scaling factor you want (e.g. 2):

<key name="scaling-factor" type="u">
<default>2</default>

3) Apply the changes:

sudo glib-compile-schemas /usr/share/glib-2.0/schemas

It works with gdm using x11, not sure about Wayland.