Baseline (Widescreen) Solution & Issues
Widescreen Solution
Step 1: Download ThirteenAG's widescreen hack at http://thirteenag.github.io/widescreen_fixes_pack#flatout2.
Step 2: Extract the .ZIP file's contents to the base installation directory of the game.
Step 3: Create a shortcut to the game, then edit the properties of the shortcut. Under "Target", add a space at the end, then type: -setup
Step 4: Use this shortcut to enter the display options menu.
Step 5: Select the appropriate resolution and aspect ratio under "Display Mode" in the window that appears.
Step 6: Once you have everything the way you want it, click OK to close the menu.
Step 7: Start the game normally. The fix will be applied while the game is running.
NOTE: You will only need to do this method once. The fix will be applied every time you start the game after you complete these steps.
Widescreen Issues
When running in 16:10 and 16:9 resolutions, the 2D elements of the main menu and pre-race menus are stretched, and the car in the vehicle selection menu is Vert-.
The FMV cutscenes that appear when you start up the game are still stretched, due to being originally created for a 4:3 aspect ratio.
Ultra/Super-Wide (21:9/32:9) Specific Solution & Issues
Strangely, the menu buttons and foreground are rendered in 4:3 and off to the left. Also, the 2D background is stretched and the 3D cars in the selection menu are Vert-, just like the other aspect ratios.
Eyefinity / Surround Specific Solution & Issues
4k UHD Specific Solution & Issues