Baseline (Widescreen) Solution & Issues
Select your resolution from the in-game options and restart the game to apply. Although most of the gameplay is Vert-, some areas of the game (bonnet cam, garage backdrop) are strictly Hor+ ! 2D screens stretch. Stretched 3D preview in Tuning mode.
Ultra/Super-Wide (21:9/32:9) Specific Solution & Issues
Eyefinity / Surround Specific Solution & Issues
Native, HUD stretch, "mostly Vert-" gameplay.
Zooming out in free camera views makes the game a lot more Hor+ than Vert-.
4k UHD Specific Solution & Issues