The 2 files you need are render.cfg and settings.cfg and can be found in the documents folder.

Example path
C:\Users\[Your Username here]\Documents\WB Games\Shadow of Mordor

Open render.cfg with notepad or other text editor and find the setting "AspectRatioLock" and change whatever number behind it to 0.

Like this
"Render.Setting.AspectRatioLock" "0.000000"

Then open up settings.cfg

There are 3 settings to change here.
Set screen height and width to your preferred values

Example
"ScreenHeight" "1080.000000"
"ScreenWidth" "1920.000000"

And then change
"Windowed" "0.000000"
And replace the first 0 with a 1 or 2

0 is for full screen that probably won't work properly if you already have issues (the game seems to dislike widescreen VGA monitors and multi monitor setups)

1 runs the game in a window

2 runs the game in a borderless window that for all intents and purposes looks like full screen.

After editing the cfg files save the changes and run the game.

It solved my issues with the game and i hope it solves yours.