Hi all, first post. These fixes aren't perfect and could be improved by having the commands launch before the window manager or login starts, if someone smarter than me can do that. Please copy and paste these fixes onto forums where other people are asking if it works for you, help google find it.
Problems:
Screen is stuck sideways in Portrait mode and can't be fixed with desktop's rotational controls.
Incorrect scaling makes everything extremely small and difficult to use and read.
Fixing rotation
Open a terminal and enter:
xrandr -o right
Fixing scaling
It's worth trying your desktop's scaling setting first, but if it doesn't work (I'm using Elementary OS, scaling controls don't work), try this command:
xrandr --output eDP-1 --scale 0.5x0.5
(If the text and icons are too big, try 0.75x0.75 instead).
If that doesn't work, try with this device name instead:
xrandr --output eDP1 --scale 0.5x0.5
In the first command above, eDP-1 is the name of the display on my GPD Pocket 2, though I imagine this model name will change between different GPD devices and production runs. Under Ubuntu Mate, the model name was eDP1 instead. If the command doesn't work, you'll need to find the name of your display, so enter the following command:
xrandr --listmonitors
For an example, this is the output from my main desktop PC at home:
$ xrandr --listmonitors
Monitors: 1
0: +*DVI-D-0 1920/598x1080/336+0+0 DVI-D-0
Here DVI-D-0 is the name of my monitor, so if I were changing scaling on my main PC at home it would be:
xrandr --output DVI-D-0 --scale 0.5x0.5
Obviously entering these commands all of the time would be irritating, so you want to make these run automatically. Your desktop should have a section for commands to run at startup, copy and paste these commands into there.
Drawbacks of my approach:
When screen locks or I logout, the welcome screen is back in Portrait. If you are going with this setup, I recommend doing so with a single user machine that is set to login automatically.
Switching resolutions from native to something else doesn't display properly, so I recommend avoiding anything like fullscreen games that run in another resolution.
If anyone more skilled out there can tell me how to apply these fixes before login, that should help matters - at least with the login welcome screen - so please write below.