Baseline (Widescreen) Solution & Issues
Native anamorphic ultrawide support: black bars are present even in 16:9.
Ultra/Super-Wide (21:9/32:9) Specific Solution & Issues
Native support, no letterboxing.
Eyefinity / Surround Specific Solution & Issues
Partial support: ultrawide anamorphism.
Although gameplay is pillarboxed by default, menus are Vert- and mouse prompts are huge. You can fix this through the registry:
HKEY_CURRENT_USER\Software\Variable State\Virginia\Screenmanager Resolution Width_h182942802
Change the decimal value to an UltraWide width (basically, display height * 2.38).
4k UHD Specific Solution & Issues
Native support (letterboxed picture).