As a follow up, I have finally resolved the issue of my laptop monitor defaulting to 1.25 scaling instead of 1.0. It appears that this is controlled by the "/org/gnome/desktop/interface/scaling-factor" dconf value.
By default, it is "0" which means an appropriate scaling factor is determined by mutter or gdm... which unfortunately on smaller physical screens, it is now choosing 1.25 instead of 1.0. To prevent this, you simply need to modify this value from "0" to your desired scaling, in this case, "1".
For mutter, this was simply a matter of using gsettings or dconf to change the value:
$ gsettings set org.gnome.desktop.interface scaling-factor 1
For gdm, this was a bit trickier... on Ubuntu there are a variety of dconf files related to gdm in /etc/gdm3 and /usr/share/gdm, but modifying those didn't seem to do anything. Crazily enough I found the following StackOverflow post:
https://askubuntu.com/questions/906797/scaling-gnome-login-screen-on-hidpi-display
The solution for me was to add a gschema override file as shown below and then running the following to update the compiled schemas:
sudo glib-compile-schemas /usr/share/glib-2.0/schemas
Ideally, there would be a graphical or more straightforward way to set the desired scaling factor... but at least it's possible to change!
#ubuntu #gnome #mutter #gdm